Thought experiments ii

["james cunningham" <pdjamesc@hotmail.com>]

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Is Conceivability a Guide to Possibility?

Parte Ye Seconde

The Circularity Objection

The circularity objection is that:

?Conceivability is a guide to possibility only as constrained by prior modal 
information tantamount to the information that p is possible?i

There are various versions in which this general form of argument is 
applied. Firstly since conceivability is not an infallible guide to 
possibility, it may fail in any given case. Allowing this it is premature to 
draw any conclusion from conceivability without prior assurance that it does 
not fail in that case, or in other words the conceivability of p is only 
evidence for its possibility if it can already be demonstrate that p is 
possible. The argument for conceivability becomes circular. However the
argument is only satisfying if conceivability does not generally indicate 
possibility. The argument can be strengthened. It is possible that a would 
not find p conceivable had he known p was impossible. The evidence in favour 
of p being possible, a finding it conceivable, is dependent on as ignorance 
and is inherently untrustworthy. For a to be certain that his evidence is 
trustworthy he must know that p is possible, and so the circularity is 
re-introduced. The argument rests on the notion that if one were to know 
that a proposition were impossible then one would not find it conceivable. 
But there is no reason to think that this will reduce the reliability of 
ones modal intuitions. The final form of the objection is that one cannot 
infer to the possibility of p without first ruling out the alternative 
explanations for the conceivability of p. To rule out the possibility of 
ones conceiving p as possible being a result of ones failing to know p is 
impossible, one must first know that p is possible, and so again the 
argument for conceivability is circular. This objection seems to put an 
unwarranted strain on any evidence. The key thesis is that one may not infer 
from evidence until one has ruled out all possible alternative explanations 
for the evidence. This would require me, for example, before accepting the 
evidence of my eyes that Bob Hale is a human, to first rule out the 
possibility that he is a well-disguised panda. Objections give an account of 
how actual conceivability errors may arise but they are silent on whether or 
not these errors arise with any regularity. The circularity objection 
therefore requires some additional premise that conceivability errors are 
common. A different formulation of the circularity argument takes the above 
arguments and turns them on their heads. If a proposition p is conceivable 
to a by dint of a being unaware that it is impossible, and since many 
impossibilities are not known to a, then many impossibilities will be 
conceivable. If this is the case then before relying on a
case of conceivability to give evidence for possibility one must first have 
a reason to deny that:

1) Although you are unaware that p is impossible, p is impossible.

1)'s first conjunct is uncontroversially true, and so 1) can only be denied 
by denying the second conjunct. But to deny this one must already be aware 
that p is possible. Even if on accepts all that is said above the thesis 
that conceivability provides a guide to possibility is still justified if p 
the fact that is conceivable allows one to conclude that p is probably 
possible. It may be argued that some of the responses to the circularity 
objection place an unfair burden of proof on the objector. It is not for the 
objector to prove that modal intuitions are not generally accurate but for 
the defender of modal intuition to prove that they are. Thus the defender 
must still be able to verify his intuitions without resort to intuition.

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