Kai-man Kwan
SB=Swinburne                                SE=sense experience 
RE=religious experience                 TE=theistic experience           

In his book The Existence of God, Richard Swinburne presents an argument from RE which utilizes an epistemological principle which is dubbed the Principle of Credulity:
(PC)     If it seems to me that x is present, then it is rational to believe that x is present unless there are special considerations to the contrary.

SB argues that it is a fundamental principle of rationality apart from which we cannot provide any noncircular justification of either ordinary perception or memory.  Then using this principle, SB formulates the following argument for the existence of God:
A) It seems to me that God is present.
B) There is no good reason to think either God is non-existent or not present.
C) Hence it is rational (at least for me) to believe that God is present.

        Michael Martin, the energetic critic of theism, raises several objections to SB's argument in an article which appeared in Religious Studies in 1988.  He repeated those criticisms with a little elaboration in his book Atheism as well.  In the following sections I would look at his objections one by one & try to give some reply to Martin.

Michael Martin & the Negative PC
        Michael Martin raises the objection that if we grant the PC, we should also grant the negative PC (called the NPC).  For example, we can formulate a NPC in this way: If it seems (epistemically) to a subject S that x is absent, then probably x is absent.  Then we can appeal to the fact that many people have tried to experience God & have failed.  Given the NPC, this should be good grounds for the non-existence of God.(pp.82-3)  Hence SB's approach will at best result in a stalemate.  According to Martin, the reason SB discounts experiences of absence of God as prima facie evidence for non-existence of God is as follows: in the case of a chair one can know under what conditions one would see a chair if a chair was there.  But we don't know under what conditions[1] one would see God if God existed.  Martin indeed thinks this is correct but he maintains that given this fact, both the PC & the NPC would be undermined.  (I would discuss this last claim in a later section.)
        I don't think that Martin's challenge here is successful.[2]  The reason for favoring the PC while disowning the NPC is rooted in the asymmetry between positive & negative existential statements with respect to empirical verification.  Let C be the claim that there is a cow & -C its negation.  For C to be true, we just need any one alleged perception of a cow to be veridical.  However for -C to be verified we need to examine all spatio-temporal locations & perceive no cow & all these infinite number of perceptions have to be veridical.  Let me call the spatio-temporal location within which a subject can normally make reasonable perceptual judgments his perceptual space.  The NPC is only tenable when it is confined within the perceptual space.  (Perhaps this is why Martin formulates his NPC using the predicate 'absent' rather than 'non-existent' but he slides easily from God's absence to God's non-existence.)  Let us try a confined version of NPC:
If it seems epistemically to a subject S that x is absent from his perceptual space, then it is prima facie evidence that x is absent from that perceptual space.

If this formulation is better, then when one reports an experience of absence of X, it only has evidential force against the presence of X in his perceptual space at the moment he makes that claim.  It can't be taken striaghtforwardly as evidence against the existence of X in contrast with X's presence in that space.  The case is different in a positive experience of X.  Whenever the claim is made under whatever circumstances, it is evidence for the presence of X in the perceptual space at that moment ceteris paribus.  Of course, it could be argued that X cannot be present in that space & hence that experience has to be illusory.  This is what happens when one's sighting of John in London is discredited by overwhelming evidence that John could not be there at that time: say, a hundred people testify to hearing John delivering a lecture in UCLA at that time.  The point here is not that positive experience of X is infallible.  The point is that if undefeated it is evidence for X's presence there & also automatically evidence for X's existence.  This transition is not possible for a negative experience, save for a being whose perceptual space is unlimited.  For a finite being whose perceptual space is limited, an experience of absence of X in that finite space is not straightforwardly evidence for X's non-existence.  However, the transition can be made if a further premise is adduced: that if X exists, then (probably) X should be present somewhere in that perceptual space (PS).  The argument can be phrased in this way:
A)        In my perceptual space, I experience an absence of X.
NPC)   Ceteris paribus, an experience of absence is evidence against the presence of X within that PS.
B)       Hence I have evidence against the presence of X in that PS.
C)       If X exists, X (probably) should be present in that PS.
D)        Hence I have evidence against the existence of X, ceteris paribus.
It should be clear why non-existence of anything is quite hard to prove.  Everyone's perceptual space is severely limited.  This can be partly remedied by a communal effort & a continuous search.  This means we can build up a collective perceptual space through mutual communication & trust.  One can also change one's PS by simply moving one's body or by launching a rocket.  In this way one can check one PS after another.  However, numerous uncertainties are there: we can't be completely sure of others' honesty or competence; in moving from one PS to another, our limitation is only partially overcome: we still cannot embrace both at the same time.  It is possible that when I move from PS1 to PS2, X has also moved from PS2 to PS1.  In this way, my experiences of absence of X in both PS1 & PS2 could be accounted for.[3]  So in view of these general considerations, it seems justified to say that the existential import of the PC can normally outweigh that of the NPC, ceteris paribus.

        Even in the case when we have a right to adopt this confined NPC, the result we get is not as certain as that we get by applying the PC.  "This is because for the positive judgment to be reliable only one causal chain needs to go from the object apparently perceived to the subject who seems to perceive it.  But if the negative judgment is to be reliable, causal chains need to go from all places where the object might be to the subject who seems to perceive that the object is not present."(SB 1988, p.294)  Consider the two claims: "there seems to be a needle in the room" & "there seems to be no needle in the room".  Which will you trust more? 
        It is also the case that at each time the effective PS of a subject can be much less than the normal PS.  For example, there is the problem of attentiveness.  One's PS is normally defined by one's capacity: it is the region in which one can reasonably make perceptual judgment.  This 'can' is predicated on the assumption of a proper exercise of the capacity.  However, one important factor which influences the proper exercise is attention- a sort of mental alertness directed to some region.  Now if one is suddenly absorbed in thought or carried away by a day-dream, then his effective PS would be greatly reduced even though the normal PS is much larger: his eyes are good & there is bright sunshine.  It is common experience that in such a situation you can approach him & remain undetected until you are almost right in front of him.  Hence when one reports an experience of absence, we can never be sure that this experience is not due to inattentiveness.  Of course we can ask him & check it.  But this factor still complicates the experience of absence & points to the fact that one's effective PS can be much less than one's normal PS.  It is different in the case of a positive experience.  It is perhaps an analytical truth that when one experiences X, one's attention is on X. (cf. Moser)  It does not mean that one has to put in mental effort to achieve this attentiveness.  In many cases a positive experience just arouses & sustains the attention.  So in a way, the factor of attention is automatically provided for by the positive experience.  The case is different in an experience of absence: normally the attention has to be kept by the person himself by an effort.  Of course, the degree of effort needed varies with a lot of factors. Sometimes an absence can be very conspicuous in cases of great interest & expectation, e.g. the absence of the bride from an arranged wedding.  In this case, not much effort is needed to detect the bride's absence.  In general, attentiveness is conditioned by interest & willingness.  When you are talking to a person you find very boring or you are conversing on a topic you don't want to engage further in, you have an uncontrollable lapse of concentration & hence can't hear properly at all!  So experience of absence is equally susceptible to psychological explanation, say, sometimes even when you can perceive X, you don't because you don't want to.  Interest is often taken to be detrimental to a veridical experience.  It is true that sometimes you seem to perceive something nonexistent simply because you want to see it.  But interest is by no means always detrimental: indeed a certain amount of interest is essential for veridical experiences.  Anyway excessive interest could blind one to genuine presence as well as create delusory sense of presence.

        There is also the problem of the perception of transient objects whose appearance is hard to predict.  It also seems that the PC would take priority over the NPC in this type of perceptions.  Let us take the example of shooting stars.  Suppose on a certain night several observers deliberately set out to watch for shooting stars but they all reported the experience of 'the absence of shooting stars'.  However another person reported that at certain time during that night he just happened to look at the sky through a window & saw a shooting star.  All the reports clearly are relevant to whether there has been some shooting stars on that night.  The former reports are certainly some counter-evidence.  However, it seems that this is outweighed decisively by the positive experience.  (Assuming all are sincere reports.)  If this intuition is correct, then it justifies my claim that the PC takes priority over the NPC here.  The relevant factor here seems to be the 'elusiveness' of shooting stars.  It is hard to predict when they will appear & from which direction they come.  Its appearance lasts hardly more than a few seconds.  These factors easily explain why it is more difficult to come by an experience of such objects.  So it also points to a real possibility that we can have experiences of absence of that object while it is actually present.  However these factors in themselves are not reasons for thinking that the reported experiences of such 'elusive' objects are delusory.  We have to make the distinction ./. the low probability of having the experience & the low probability of the veridicality of that experience, given that somebody has that experience.  The 'elusiveness' of an object would count towards the former.  However, it does not count towards the latter unless the existence of such 'elusive' object is a priori improbable.  I see no grounds in making this claim.  Surely there is a common bias towards extremely stable objects like a table but I submit that there is no reason why a real object has to be like a table.  A table is a paradigm of a manipulable object & it is natural that in our technological & materialistic culture we have a bias against anything that can't be controlled & manipulated.  It is also reflected in the epistemological move which makes perception of a table & the like the paradigm of perception.  I have no objection if 'paradigm' is interpreted as a model of excellence but so often it is taken to be a model of minimum requirement.  Sometimes philosophers move imperceptibly from one to another & vice versa, & I think it generates a lot of confusions.  Furthermore, contemporary science has already moved quite far from our stable tables in the search of the real.  The atoms, the wave functions , etc. also seem quite elusive.  Some fundamental particles also have an extremely transient existence but they are no less real for that.  For example, neutrinos are by nature very elusive: they are very hard to detect.  Suppose we devise an experimental set-up to detect the presence of neutrinos.  In one experiment the result is positive & in another the result is negative.  Further suppose that if any of this is spurious, we don't have any explanation.  It seems plausible to claim that the positive result is more significant than the negative one. 
        I am not saying that God is like any of the above things.  If God exists, He is of course as stable as any object can be.  However, He can be elusive with respect to our experience of Him: He cannot be manipulated like a table can be.  What I say only serves to point out that the ontological bias towards stable & manipulable objects itself stands in need of justification.  As a summary, I propose the following principles to arbitrate between the PC & the NPC:
P1)       With reference to existential import, PC usually outweighs NPC.  (Because our PS is inescapably finite.)
P2)       All other things being equal, reports of experience of absence of X would not outweigh reports of experience of presence of X; the latter normally outweigh the former.
P3)       All other things being equal, if X is an elusive object, then reports of experience of X would normally outweigh the reports of experience of absence of X.
An elusive  object is one which we can't manipulate & cannot experience it at will.  It may be so because of its transient existence; or else it is due to the unpredictability of its behaviour & its appearance.  A shooting star is elusive due to both reasons.  A person can be elusive due to the second reason alone.  Consider the following story.[4]  During war time, I had the experience of a secret agent who frequently appeared mysteriously to me alone & then disappeared after a short while.  No other people seemed to have similar experiences.  Certainly this secret agent is elusive but does it mean that it is more probable that my experience of him is unveridical?  Does the fact that others lacked similar experiences discredit my positive experiences?  I think not. 
       Now can we apply the above considerations to experience of absence of God?  (P2) seems also applicable here.  In general reports of experience of absence of God are still open to more defeaters than reports of experience of God.  (P3) also seems applicable to God because God is also an elusive object of experience in the sense that his personal nature & sovereign freedom make an experience of Him unmanipulable by us.  The application of (P1) is not so straightforward.  It is because the idea of a physical PS is not applicable to God.  If it is, then it could be argued that since God is everywhere God should be present in the PS of everyone all the time.  This would make the experience of absence of God even harder to explain from the theist's perspective.  Again the clue seems to be the personal nature of God.  So let us look closer at the realm of interpersonal experience & I would argue for the coherence of the idea of an 'interpersonal perceptual space'.  I suggest this idea models better the perceptual relationship of man & God & given this idea we can see that though God is omnipresent, He is not automatically within everybody's perceptual space.   If this is correct, then (P1) would also apply in the case of God.
         Here I would talk about experience of other persons & experience of their inner feelings.  I am aware that this would engender some misgivings & so let me explain what I mean by these expressions.  First of all, it might be objected that experience of other persons' feelings is impossible because one can never really experience others' feelings from inside.  Well, I think it is also true that one can never see a table as the others see it.  What I mean by an experience of others' feelings is: 1) it epistemically seems to me that they have such & such feelings; 2) this epistemic seeming is accompanied by (or connected with in a more intimate sense) appropriate sensory content & feelings.  This seems eminently possible: the experience may be unveridical but as experience it is still real.  Surely there is merit in emphasizing that a first personal experience of feelings is primary & it transcends a second or third personal experience of them in many ways.  But the latter is still possible & important in our lives.  (It is part of our predicament that we desperately want to communicate our feelings but find the attempts constantly frustrated, at least partially.)  Now let us consider a subject S's experience of another person T.  Surely S is prone to make some judgments about T & these judgments can also be reasonable or unreasonable.  It also seems that judgments about T can be more or less superficial: judgments about T's appearance is more  superficial than judgments about T's inner life.  (I know that my talk of inner life would offend some philosophers but I would not apologize for it.  Any person who has some in-depth experience with another person will recognize that there is a depth to another person which is hardly deducible from or reducible to his or her outward appearance or behaviour: past traumatic experiences, secret wishes, inner struggles, & so on.)  So let us talk about an interpersonal PS of S with respect to T , IPS(S,T), as the scope within which judgments about T can reasonably be made by S.[5]  What factors influence the size of IPS(S,T)?  Three things, it seems: sensitivity & maturity of S, openness & maturity of T, & their relationship.
1) S: it is obvious that if S is more sensitive to personal experiences he can make more reliable judgments about deeper aspects of T.  This sensitivity needs to be built up by life experience & a willingness to be open to others' experience.  If one is consistently open to other persons & has rich experiences with other persons, then we can expect him to develop a higher sensitivity which is manifested in two aspects:
a) S can judge more reliably given a certain basis of information about T.
b) S can pick up cues which are hardly noticed by the less sensitive people.
        It also seems that sensitivity is both a matter of mind & heart.  It involves a richer repertoire of concepts about personality, mental states, feelings as well as larger capacity to experience those feelings & mental states, e.g. anxiety, depression, suppressed hatred.  Reason & emotion can hardly be divorced in this case.  A sensitive person needs both acute intellect & empathetic personality.  Without the latter endowment, the former is hardly applicable to the realm of interpersonal experience.  (Ex.: a callous super-scientist.)  Without the former, the person can still be a good listener & comforter but can't make reliable judgments & this may hamper a full, two-way communication.  Nobody is born a very sensitive person.  It is attained in a process of maturation & hence sensitivity is also tied to the maturity of the person. 

2) T: every person can be characterized by a tendency to be either open or closed.  Some are so open to everybody that he is almost transparent.  Some persons are so closed to everybody that we can have access only to the surface of his inner life.[6]  In this case no matter how sensitive is S, IPS(S,T) would still be very small.  Sometimes the obstacle is not T's openness but his maturity.  We all may have  the experience that while we want to express our feelings & inner life, we just don't know how to communicate.  This inability may be overcome by a maturation process after which T can grasp his feelings more accurately in a  more articulate manner.  However, this process is again dependent on whether T encounters some sensitive & mature persons which want to understand him.  This is a very strange fact about interpersonal experience: our maturity seems to depend on one another.

3) Relationship: so the most crucial factor seems to be the relationship ./. S & T.  The prior sensitivity of S & prior openness of T are independent factors but these might be greatly modified by the relationship.  Hence the relationship is not only a function of two independent variables S & T: it also creatively transforms S & T.  Each relationship is in a sense unique.  Take some examples.  S may be in general a very sensitive person but towards an individual T, he may not be sensitive at all.  It is even possible that the relationship ./. S & T is so strained that S comes to have gravely distorted perceptions of T.  On the other hand, T may be a very closed person in general but there may be a unique person, S, whom he trusts enormously & to whom he discloses almost every thought & feeling.  So IPS(S,T) does not only depend on S & T but also greatly depends on the particular relationship ./. S & T which further hinges on the whole history of their interaction.  Typically when S & T just come to know one another, IPS(S,T) would be quite small.  If the relationship grows in mutual goodwill, then IPS(S,T) would be enlarged.  It means not only S knows more about T's inner life; it also means that S is more capable to understand T's motive & interpret T's cryptic sayings & the like.  An ability or a disposition is built up.  This does not seem to be easily transferable.  It is difficult for S to transfer his knowledge of T to S': much of it is tacit & unverbalized or unverbalizable.  Even when such knowledge is transferable, it is dubious that S' would thereby be enabled to know T as well as S does.  The information might be transferable but the ability is not. 
        Relationship is a tricky matter.  Rarely there is linear progress.  IPS may well dwindle because of conflicts & prolonged misunderstanding.  An enlarging IPS depends on mutual trust & willingness to see & feel things as the other sees & feels.  This is by no means easy & sometimes to avoid it one may just assert one's viewpoint (perhaps it is threatening to one's self-image) & denies the validity of the other's. 
        It is also the case that the effective IPS is only the subset of the normal IPS.  Even when a husband should be able to understand the implicit complaint of his wife, it may not be true in a particular case.  He may be simply inattentive or lacking in care.  On the other hand, even when two persons have developed a very close relationship & the normal IPS is quite large, T may deliberately withhold some feeling from S on a particular occassion for some reason.  In both cases, the effective IPS would be reduced at that point & either S or T can effect this reduction. 
        So if my concept of a IPS is intelligible, then let us use it to illuminate a subject S's experience of presence or absence of God.  Let G stands for God & let us consider IPS(S,G).  The problem is that for some S, IPS(S,G) is an empty set.  How are we going to explain it?  (cf. Davis, p.99)  The first thing to be noted is that God is an immaterial person.  Whereas embodied persons are tied to a certain physical body & some of their mental states are more or less linked to observable behaviour, it is not so for God.  This means that when we are in contact with an embodied person T, we can make judgments about T in a quite detached way without involvement & commitment.  Hence even when S is not interested to know T, IPS(S,T) is rarely an empty set.  (It should be clear that in this case, IPS(S,T) would hardly be more than a small set.)  It is different with God.  When we feel God's presence in any intimate way[7], we are also entering into a relationship with God.  However, to acknowledge this presence would entail a lot of change in self-understanding & worldview, isn't it natural that some people who are unwilling to do so would suppress this feeling?  (cf. Kellenberger)  There are also many cases when people are just totally absorbed in secular concerns & egoistic pursuits.  Their experience of the absence of God can be easily explained by their sheer inattentiveness.  However the problem is more serious in two cases: 1) when great evils occur, a loving God is expected to intervene & let His presence be felt, & 2) the honest & arduous seekers after God which fail to experience God.  The former does need some explanation but I can't go into theodicy here.  In the latter case (e.g. Michael Goulder), we can never be sure that one is completely honest.  However, perhaps we should also see the problem from God's side.  When people are not ready or willing to experience Him, God's refraining from imposing His Light on them seems eminently understandable: just respecting their choices.  However, when the people are willing, what 's the right time to reveal Himself?  Not all seekers immediate experience God: the process can be very long & the search contributes to the richness of the personal life & human experience.  God sometimes seems to act in dramatic ways.  It does not obviously seem to be a greater good that God immediately & mechanically reveals Himself.  It is not due to God's capricious feelings but due to His creativity & 'strange ways'.  As a summary, when IPS(S,G) is an empty set, several reasons are plausible: 1) S's inattentiveness reduces it to empty set or 2) S is unwilling to enter into a relationship with God & God respects this freedom or 3) though God will reveal to S, it is not yet the right time.  For example, while God is anonymously guiding S, God knows that it is better to reveal more explicitly to S after S has a certain personality development or 4) not everybody needs to have 'emotional' experience of God; a faith that is nurtured on other grounds  is possible for S. (?)
        Now suppose we still have residual cases which are hard to explain in this way.  I think it is probably true but what epistemological relevance does it have?  I still think that the PC would take priority over NPC in this type of interpersonal experience.  In general, IPS(S,T) depends on both S & T & a lot of other factor.  For example, suppose we are considering the case whether T has a traumatic memory which causes him a deep sorrow.  It is typically difficult to know whether it is true from the outside & it is also difficult to predict under what circumstances he would display it in behaviour or discloses it verbally to someone else.  So if S lacks any such experience, it is not very good evidence for the thesis that he has no such traumatic memory.  On the other hand, if S has such experience of T's disclosure, then it is pretty good evidence that T has such traumatic memory.  Now if God is conceived as the Supreme Person, then isn't it presumptuous that we can predict when He would make such & such a revelation?   So on analogy with our ordinary interpersonal experience, it is plausible to claim that experience of absence of God is less significant than experience of God.  Besides the lesser scope & force of the NPC, let us further consider the intricate factors which contribute to the reduction of IPS, the sovereign freedom & immensely higher wisdom of God, the good of dramas of life & so on[8].  I submit that even a single experience of God is not outweighed by a single experience of absence of God, ceteris paribus.  Furthermore, it seems to me the proportion of seekers who succeed in finding God is higher than those who fail.  Perhaps the successful seekers are self-deluded.  It seems that the sceptic must adopt some similar explanation to explain away the experiences.  Now if it is a must, then there is no reason why we can't explain that there is also delusion in those failed 'seekers'.[9]  Though I feel quite uncharitable in proffering this explanation, I find that this is forced on me in some sense: the successful seekers & the failed seekers can't be both right.  Whereas the atheists have to interpret the 'successful' seekers as being deluded, the successful seekers actually do not need to do the same: they may just appeal to God's inscrutable ways with men & the unfathomable mystery of every relationship, & to the future revelation of God to those honest seekers.  If the atheist finds this unsatisfactory, then he may well consider the above uncharitable explanation.  Perhaps the seekers are just curious & they never intend to develop a serious relationship with God?  Perhaps despite their surface claims, they have unconscious desires to avoid God?  Perhaps ...  If I am right that there are more successful seekers than failed ones & if the less people are deluded the more charitable the interpretation, then perhaps we should better accept that it is the failed seekers who are deluded.  Hence arguably even in that case evidential force of REs will only be lessened & not cancelled completely. 
        So this objection of Martin fails.

No Criteria Objection
        The most common criticism of SB is the claim that the PC is only applicable when we have rational criteria to distinguish the veridical experiences from the unveridical ones.  For example Rowe repudiates SB's PC & formulates this one instead:
"When subjects have an experience which they take to be of x, & we know how to discover positive reasons for thinking their experiences delusive, if such reasons do exist, then it is rational to conclude that they really do experience x unless we have some positive reasons to think their experiences are delusive."(p.91)[10]

        Martin presses a similar objection & he is clearer in his rationale.  He alleges that "neither PC nor NPC should apply unless one has a right to assume that perceptual conditions hold under which the entity at issue is likely to appear to an observer if the entity is present.  This right may be justified on inductive grounds, by one's background theory or in other ways." (pp.85-6)  Consider ordinary perception first.  Let T be "there is a table in front of me" & C1 be "a certain perceptual condition" & A1 be "a table appears to S".  That the PC is applicable in such a case is because we know:
(1)       If T & C1, then A1.
(5)       If -T & C1, then probably -A1.
So given -A1 & C1, then -T.  Also given A1 & C1, then probably T.  That is why "a table appears to S" is good evidence for "there is a table" & why "there is no table appearing to S" is good  evidence for "there is no table before S".  However in the case of alleged perception of God, the conditions under which God will appear to S, if he exists, are unknown.  In this case no argument similar to (1) & (5) above can be offered.  "In our ignorance it surely seems illegitimate to suppose that an appearance of God is grounds for supposing God exists."(p.85)  So Martin is claiming that the PC is not a fundamental principle of rationality.  It is only applicable when we can offer inductive grounds or other support for it in certain cases.
        This is a very common & important objection which deserves to be dealt with seriously.  Let us come back to Rowe's objection first.  We must ask why does absence of criteria matter & what sort of criteria are relevant here?  As it stands the claim that there is no criterion at all to distinguish the veridical REs from the delusory ones is false.  Consider such criteria (Losin, p.66):
a) good consequences: leading to or reinforcing a new life marked by such virtues as wisdom, charity & humility
b) effect on others
c) depth, profundity, & the "sweetness" of the experience
d) agreement with orthodox talk
e) resemblance to paradigmatic mystical experiences
f) consideration of pronouncements of authority
It is just not true that the God-experient will accept every experience of God as veridical. 

        However, it may be replied that there are no external & non-circular criteria.  All such criteria depend heavily on religious beliefs which are supposed to be justified by REs.  For example, Martin comments on the test of scriptural compatibility & asserts that it won't do because it "already presumes that the Bible is the revealed word of God & therefore that the Christian God exists, it cannot be used to support an argument from RE for the existence of God." (Atheism, p.160) 
        So though Martin doesn't "wish to deny that (PC) operates in ordinary life & science", he thinks "there are more limitations on its use than Swinburne imagines, & they need to be more tightly drawn". (Atheism, p.186)  His aim is to restrict the PC so as to reject REs while avoiding scepticism.  The basic restrictions he proposes seem to be twofold.[11]  Firstly a necessary condition for the PC to be applicable is that we have knowledge of the perceptual conditions of veridicality of a kind of perception: "For example, in order to be able to justify my spontaneous perceptual belief that there is a brown table in front of me, it would seem to be necessary[12] in principle to be able to argue thus: Spontaneous beliefs of a certain sort occurring under certain conditions are usually true, & my belief that there is a brown table in front of me is of this sort & occurs under these conditions.  Consequently, my belief is probably true." (Atheism, p.157; italics mine.)  Secondly, another necessary condition is that there are tests for veridical or unveridical perceptions which are non-circular.  This requirement should be clear from the above quote on 'the test of scriptural compatibility'.  Now Martin is right that were we to subscribe to such criteria, the independent evidential force of REs would be greatly endangered.  Yet it is not clear that Martin's sanguine claim that "this would not result in skepticism about ordinary objects" (Atheism, p.185) is then justifiable. 
        The reason is that all criteria used for sifting away the unveridical perceptions depend upon sensory experiences & assume anyway the existence of the external world, the "thing" framework, & so on.  Take again Martin's example of seeing a table.  Consider premise (1): If T & C1, then A1.  Presumably C1 will include "the lighting is normal" &  "S is attentive & his sensory equipment is functioning normally".  We must ask how do we come to know (1) by induction.  I think the answer is something like this: "We observe that in many cases when there is a table & the lighting is normal & S is attentive & his sensory equipment is functioning, we hear S telling us that he appears to see a table."  The problems become crystal clear as soon as this answer is spelt out.  How are we supposed to know any of these things without assuming some of our perceptual claims are at least "innocent until proven guilty", not to mention the problems of justifying our interpreting some sounds emitted from a body as a testimony?  Furthermore, for the argument to be completed, we also need to assert that C1 actually obtains.  Again how on earth are we going to know it?  It seems that we can only check the lighting by our eyes.  We can check our attentiveness by introspection.  We could check our sensory equipment by doing some surgery but it is rarely done in practice.  The problem of vicious circularity still remains: if I need to justify my application of PC to my 'seeing the table' by further premises & inference, by parity don't we also need to justify the premises in the inference?  They seem to belong to the same type of perception which is in need of justification.  This problem is so obvious & familiar that I find it very surprising Martin never tries to bring it out.  When further arguments & illumination are required, he simply asserts that "knowledge is available about when chairs will appear if they exist" (Atheism, p,185; italics mine)  He also assures us that there are "various ways" in which "the skeptical questions" can be "silenced". (Atheism, p.186)  These claims are totally mystifying to me & I wish Martin had spelt them out.  Certainly a theory 'about when chairs will appear if they exist' is available.  It is just not clear how this theory can be transformed into knowledge.  Perhaps there are ways that skepticism can be defeated but it does not seem likely given the above necessary conditions of application of the PC.  It looks as if Martin is so eager to defeat REs that he unhesitatingly lays down the above stringent conditions.  But when the skeptical consequences begin to loom large, he simply asserts or hedges.  Perhaps my interpretation is unfair but anyway Martin still owes us an account how he can hold to both the application of PC to ordinary life & the above conditions of applicability.  In the meantime, we are justified to ask the question: "how (1) or (5) are to be known?"[13]  to which Martin does not give any answer. 
        However, let us try to explore further the possible answers to the above question.  In the above paragraph, I have briefly discussed the possibility that (1) is established by induction.  This seems hopelessly circular.  Another answer could be that the relevant criteria are conceptually derived from the ontology of physical objects in space-time.  Gale seems to adopt a similar line.  He argues that all the relevant tests can be derived from the nature of physical objects & space-time.  His discussion certainly shows further the coherence of SE but it is dubious he has shown more than that.  He argues that if physical objects have such & such nature, the tests for veridical SE can then be derived.  However, it still does not show that when those tests are passed the SE in question is then proved veridical.  Such coherence in itself does not rule out the sceptical alternatives.  Perhaps the evil scientist is also a good philosopher: he first lays down some ontological descriptions of the nature of 'physical objects' & then derives the principles which govern the 'veridicality' or 'unveridicality' of SEs.  These principles are then used as the most basic axioms of his program which governs the inputs to a brain-in-a-vat.  (Of course he also needs to draft some contingent causal laws which conform to the axioms.)  In this way all the experiences of the brain-in-a-vat would indeed conform to Gale's theory of SE.  Perhaps the brain-in-a-vat also reasons as Gale does & concludes that all his experiences must be real?  This would only make the evil scientist laugh!
        It is a further question how Gale's understanding of physical objects is derived from the first place?  Perhaps we can rely on the grasp of some a priori necessary truths.[14]  But the experiences themselves are also indispensable.  Without prior trust in those experiences, can we trust the theory derived from them?  Again a vicious circularity threatens. 
        Let us look at some more concrete example.  We seem to see a bending stick when part of a straight stick is immersed in water.  We would count that an illusion while taking the perception of the straight stick as veridical.  This distinction is taught to us since our early days & most of us would take it for granted.  But can we give an account of the reasons for this move?  Let us not first take into consideration of the science of optics.  If the optical account of the illusion is necessary for the above distinction, then we are denying the right of most of our ancestors to make this distinction.  This seems most implausible.  If we just consider the more common sense response, then probably most of us would perhaps say that the reason why the apparent perception of a bent stick is illusory is as follows: "If we take the stick out of the water, the stick again looks straight.  Furthermore, if we grope for the stick partly immersed in water, it still feels straight.  Therefore it must remain straight although it seems to be bent."  Now it has to be noted that this account is by no means the only possible one.  For the first reason to be conclusive, it has to make two more  assumptions: firstly, the visual perceptions are veridical; secondly, the shape of the stick has remained constant throughout the process.  If we are prepared to grant that the stick is bent when it is partly immersed in water & it is straight when all of it is out of the water, then we can insist that both perceptions of a straight stick & a bent one are veridical.  The tactual experience by itself is compatible with this account: we can insist that vision is more reliable than tactual experience.  Now the tactual experience & the visual experience of the stick partly immersed in water seem incompatible[15] with one another.  Why can't we take the tactual experience as illusory instead of the visual one?  I take it that it is difficult to establish conclusively that this re-interpretation must be incorrect.  It seems to me we choose the common way of interpretation because we have presupposed two rational principles:
Other things being equal, we should choose an interpretation of experience which fits with the simpler ontology.

Other things being equal, we should choose an interpretation of experience which would render more of our perceptual experiences veridical.

        The second principle in itself is not sufficient: both interpretations would need to render some experience illusory & it does not decidedly favor the common sense interpretation.  However, the common sense interpretation posits a sort of stick which would not suddenly change shape when immersed in water & this ontology is simpler.  Someone may object that a stick is just not the type of object that would easily change shape.  This piece of knowledge, it might be argued, is the foundation of our common sense interpretation of experience rather than my alleged rational principles.  This reply won't do.  It may seem obvious to us that the above statement about the stick is true but it is only so because it is repeatedly confirmed in our experiences.  But given that our experiences can be illusory, can we decide what is confirmed by our conflicting experiences unless we have a way to distinguish which experiences should be counted as veridical & which illusory?   The answer seems to be no.  If so, then the above principles seem to be basic principles of experiential interpretation in accordance with which we posit the veridical-illusory distinction.  The first one is effectively a form of the Principle of Simplicity.  The second can be seen to be a corollary of the PC.  If so, then the PC & the Credulity Approach would nicely account for the way we make the veridical-illusory distinction.  Now it is true that consideration of ontology comes in when we make the veridical-illusory distinction but this distinction is still prior to the knowledge of the nature of the physical world.  To gain such knowledge we need to justify it by veridical experiences & hence before we can know which claims can be regarded as knowledge we need to decide which experiences are veridical.  If the above argument is roughly correct, then the more plausible account of the 'whence' of our criteria of SE would fit in better with the view that the PC is a fundamental principle. 
        Now I want to discuss the role of science in confirming our common sense way of making the veridical-illusory distinction.  I have earlier raised the question why the visual experience is taken to be illusory rather than the tactual experience of it.  One powerful reason for this is provided by the theory of geometrical optics because it gives a more detailed explanation of the visual illusion by positing the process of refraction of light rays by water.  On the other hand, if we take the interpretation that the stick is bent when partly immersed in water, we do not have explanations why the bending occurs & how the alleged tactual illusion of straightness occurs.  However I take this to be a contingent matter.  Perhaps such explanations are not available because they have never been sought: we have already decided that the bending is not probable.  It does not mean however that it is not possible that the immersion in water would cause the bending of the stick.  It just isn't the case & this is confirmed by the scientific explanations.  So another principle seems to be involved:
If two interpretations of experience both render some experiences illusory, the interpretation which gives better explanations of the alleged illusions is to be preferred.

        Why do we need the tests?  They may be needed to provide the conceptual distinction ./. a veridical experience in that type from an unveridical one.  If it is the case, then we can further ask: "How precise do they need to be?"  The critics like Martin & Gale seem to demand that the criteria have to be very precise  & fully determinate in every situation.  (It is dubious whether the tests of SE can satisfy this demand.)  This seems unreasonable.  There is no obvious reason that for a type of experience to be roughly reliable, we must have such precise tests.  In many other situations, we can make objective distinctions without having precise criteria: legal judgment, choice of large scale scientific theories, judgments of others' personality & motive, etc.  (Ghost of verificationism?) 
        Martin also makes much of the problem of underdetermination in REs.  This is correct as far as the identification of the problem goes.  However, if Martin suggests that this would destroy the cognitive value of REs, then again he must give us an account how underdetermination does not damage induction & science.

        In the end such objections may only betray the bias that all experiences should be checkable by criteria similar to those used in sensory perception.[16]  The reply of Losin is apt: "Rowe has simply assumed that reasons drawn from experiences of God cannot themselves be "reasons for thinking that particular experiences of God are delusive," that experiences of God cannot themselves provide a (fallible & provisional) means for the critique of other such experiences.  I see no reason to think that this assumption is true, & good reason to think that, when suitably amended & applied to sensory experience, it is false.  Nor do I see the slightest reason why we cannot use knowledge or beliefs about God not gleaned from experience of God to identify & dismiss particular experiences of God as non-veridical."(p.69) 

Martin’s criticisms of the argument from RE are not convincing.

[1] This claim needs to be understood carefully.  In a sense, at least we can lay down conditions when it is probable that one would see God: a) when God decides to reveal Himself & judges that this is the most appropriate time to do so, & b) when the person is spiritually ready to see God (assuming God respects human freedom).  Of course these conditions are vague.  They are neither manipulable nor ascertainable by us.  But what is the reason to think that this renders the alleged experiences of God unveridical?  Why is it the case that the perceptual conditions of a veridical experience must be manipulable & ascertainable by us?  I would expand this point later.
[2]. Indeed I think there were adequate replies already: Davis, pp.97-9; SB 1988, p.294.
[3] One can also enlarge one's perceptual space by tools & equipment.  A stick is very useful for enlarging one's tactual space.  The other point: the perceptual space is also dependent on the modality of perception: one's auditory space does not coincide with one's visual space & both are normally much bigger than one's tactual space.  Gustatory or olfactory space is usually very limited.
[4] I owe the idea to a suggestion of Swinburne in conversation.
[5] When one makes judgments about oneself, we can talk about IPS(S,S) or IPS(T,T), a sort of introspective or reflective space.  It is an interesting question about the relation between IPS(S,T) & IPS(T,T).  It might be thought that the former has to be a subset of the latter.  This seems incorrect.  S can make reasonable judgments about T's appearance while T is less easy to do so.  Furthermore suppose S is a psychiatrist & T is his client.  It is possible that S can make reasonable judgments about some of T's deep motives whereas T is still blind to them.  But even in this case, there is still a large area of IPS(T,T) which is never accessible to S.  I tend to think that it is never the case that IPS(T,T) is a subset of IPS(S,T) except when S is God.
[6] Physical pain is actually on the surface of one's inner life.  It makes its reality so hard to deny but it also makes the Wittgensteinian analysis easier.  On the other hand, deeper mental episodes like traumatic memory would be hardly congenial to such analysis.  Hence the reductionist is likely to deny their reality, say, by adopting an attribution theory of emotions: emotions are nothing more than self-attributions or interpretations & they do not refer, strictly speaking.
[7] Perhaps there is a more 'mechanical' or 'oblique' way to feel the presence of God.  Perhaps God is present in man's moral or aesthetic experience as well.  Perhaps God is present but incognito.  I'll explore this theme in some details in ch.9.
[8] Perhaps the Christian doctrine of sin is also relevant here.  In Romans 1, Paul talks of the blinding effect of sin & the Calvinists are adamant on the noetic effects of sin.  If this is the case, then experiential knowledge of God is inseparable from the process of redemption because the human capacity of perceiving God is lost after the Fall & only restored by grace.  Perhaps it is true but in the main text I want to argue that we can have general grounds apart from the above doctrine to think that the experiences of absence of God are not significantly diminishing the evidential force of experiences of God. 
[9] It is strange that while Martin is enthusiastic with his psychological hypothesis of the experience of God, he never considers the possibility of a psychological hypothesis of the experience of absence of God.
[10]. Actually Rowe's formulation is not as careful as it should be.  In his paper he discusses some reasons for thinking that God does not exist or the experiences are delusory.  To exclude REs by his version of PC, which is his purpose, we have to interpret the "reasons for thinking their experiences delusive" as the perceptual conditions under which we are justified to think that the experiences are delusory.
[11] Martin also endorses Gutting's proposed restriction.  I also endorse it & would discuss it later.
[12] Elsewhere he says "Whether this should actually be made a condition of application is not clear."(Atheism, p.173)  This tentativeness is in contradiction with the above quote & the general tone of his objection. 
[13]. I think it is also a mistake by Martin to think that the perceptual conditions in (1) & (5) are the same.  The conditions required by (5) could be much more complicated than those in (1), e.g. including "there is no deceiving demon" & "S is not a brain in a vat."  That means C1 in (5) is almost unascertainable unless we rule out all sceptical alternatives from the very beginning.
[14] Gale indeed appeals to some necessary truths but it is not clear how he understands the nature of such necessary truths. 
[15] Actually as experiences they are only incompatible when we interpret them realistically: there is a real world with objects who have determinate properties & the experiences' propositional content should be taken seriously as indicator of the properties of those real objects.  If either presupposition is removed, it is not clear in what sense the experiences are not compatible.
[16] This is a kind of Disanalogy Objection to religious experiences & I will discuss this in full in chapter 10.