When seeing is not believing: A critique of priest's argument from perception

Abstract

In this paper I critically examine an argument proposed by Graham Priest in support of the claim that the observable world is consistent. According to this argument we have good reason to think that the observable world is consistent, specifically we perceive it to be consistent. I critique this argument on two fronts. First, Priest appears to reason from the claim ‘we know what it is to have a contradictory perception’ to the claim ‘we know what it is to perceive a contradiction’. I argue that this inference fails to be valid. Secondly, I give reasons for thinking that if an observable state of affairs were to be contradictory, we would perceive it to be consistent. As such that the world we observe appears consistent does not constitute evidence that it is in fact consistent. That we see a consistent world is no reason to believe that the world is consistent. I conclude the paper with some reflections on the implications of this analysis for the plausibility of trivialism.

Notes

²For an excellent example of this effect I direct the reader to the world wide web at http://www.sandlotscience.com/Movement/Spinning_Chevrons.htm

³That Priest has provided us with examples of perceptions with contradictory contents cannot, however, be taken for granted. It is possible to re-describe all the examples in question such that the contents are consistent and yet the strangeness of the perceptual experience is preserved. The Penrose figure can be understood as being a staircase in a space that is non-Euclidean (there is only a contradiction in ascending and returning to the same point if the space is Euclidean). The ‘water-fall’ effect can be understood as a figure or body being in motion and not being in motion in two different senses—not being in motion in the sense that they do not change position and being in motion in the sense that our sensory apparatus is disoriented. The ‘fill in’ effect can be understood not as being both green and red but as being an entirely new colour altogether. Now whether any of these re-descriptions are more plausible than those offered by Priest is a point worth debating. I think that there is a good case for the first and third, a less plausible case for the second.

⁴That we know they are illusory is because we can see they are not compatible with what others perceive. Nor are they compatible with the information supplied by our other senses [Priest 1999: 444 – 5].

⁵To view a copy of this lithograph I direct the reader to the web page of the copyright owner on http://www.mcescher.com/. The copy is to be found in the gallery of the web page under the years 1955 – 1972.

⁶Although it is important to add here that according to some versions of the orthodox or Copenhagen interpretation of quantum mechanics the measuring device does not go into a superposition. Rather the device causes the superposition of the molecule to ‘collapse’ and transform into one of the branches.

⁷Again this question only makes sense if you reject those interpretations of quantum mechanics in which there is a collapse of the superposition prior to observation, e.g., some versions of the Copenhagen interpretation.

⁸I suspect that the above discussion of non-collapse quantum mechanics is more than merely a metaphor or analogy for illustrating why we do not observe contradictory states. It might be possible in this regard to interpret a state of superposition as literally being a contradictory state of affairs, with each branch corresponding to a conjunct in the contradiction.

⁹Although for both such visual experiences the having of them does not imply that a contradiction is being observed as they can, as was argued in the previous section, be generated by consistent states of affairs.

¹⁰There is a grain of truth then behind the claim (on the part of classical logic) that explosion is a valid form of inference: Contradictions tend to spread resulting in the truth of all kinds of things that would not otherwise be so.

¹¹The mistake of confusing a denial of the Law of Non-contradiction with the Law of Non-triviality dates back to Aristotle in his Metaphysics, Γ.

¹²As has been developed, for example, in Lewis [1986]. Whether the account of possibility that I propose is acceptable will depend on how it compares to Lewisian modal realism and other accounts of possible worlds such as modal actualism and Meinongianism.

¹³I would like to thank my PhD supervisors Anthony Imbrosciano (University of Notre Dame, Australia) and Graham Priest (University of Melbourne) for their helpful dialogue concerning the topics and arguments within this paper. The critical comments of the two anonymous referees from AJP were crucial to the development of this paper and so I wish to express my gratitude to them. Last but not least a thank you to Ingrid Buckley from the University of Notre Dame for her IT expertise.