Friday, March 1, 2024


The Infallibility of Sense Perception

by Francois Tremblay

Sense perception is designated as one of the basic methods of reason. The other two are concept-formation and logic. The common trait of all these methods is that they permit us to receive and process information by extrospection. The senses receive natural inputs such as light, sound waves, pressure and heat, which are interpreted by the individual with the use of concepts and logic applied to them.

While no one denies it outright, many people misunderstand the importance of sense perception in human understanding. It cannot be emphasized enough that sense perception is infallible and undeniable, and as such rests as the inerrant foundation of rational thought. It excludes all possibility of denial or revelation as a substitute, thus debunking both religious and agnostic epistemologies.

This may seem as counter-intuitive. After all, we have plenty of instances where our senses are “wrong”. We perceive things that “aren’t there”, “illusions” and “mirages”. However, the problem is dispelled when we examine what these terms actually mean. To propose that something is an “illusion” or “mirage” presumes that we know its true nature is different. Otherwise we would call it by what we think it really is.

Take the example of the mirage of an oasis in the desert. Suppose that we have two individuals observing it, one who is aware of the existence of mirages and one who is not. Obviously the former will understand that he is looking at a mirage, and the latter will hold the belief that he is looking at some kind of lost oasis. And the knowledge about mirages was acquired through knowledge of the law of refraction, which was done with sensory data.

A mirage of this sort is observed because some light rays that come from the sky are refracted, due to the difference of temperature between cold air above and hot air below. Thus we think we see a large body of water when in fact we are seeing the sky in a different manner. We do indeed perceive the correct input, the light rays that come into our eyes: thus, there is nothing “wrong” with the perception of a mirage. What is “wrong” is our interpretation of it, which has to be based on reason, in this case on the law of refraction.

Sense perception is contextual, that is to say, it depends on the object observed, the conditions where the object is placed, and our own senses. In this example, we would observe the sky normally in most circumstances, but the extreme atmospheric conditions make it appear as a mirage.

As such, we say that sense perception is like an axiom in that it cannot be denied without direct contradiction, more precisely without committing what is called the fallacy of stolen concept. For to deny the efficacy of a percept can only be done by pointing to other percepts, thus “stealing the concept” of perception in order to deny it. To claim that a mirage disproves the infallibility of perception implies using refraction as an argument to demonstrate that it is indeed a mirage, which itself was discovered by perception.

Both infallibility and contextuality are also easily illustrated by the typical example of the “bent stick” experiment. Everyone who has taken a class in physics knows about the experiment, in which you place a straight object, usually a pen or pencil, in a glass of water and look at it from eye level. The pencil will look bent because of the different refraction indices of water and air.

We know in fact that the pencil has not been broken, because we know that submerging something cannot break it that easily, but more importantly because we can use our sense of touch to find out that it is indeed not broken. Doing so should inform us that we should have remembered the special condition in which the pencil is placed in, instead of assuming that the pencil is indeed broken.

To ignore the conditions of a percept is called naive realism. In this perspective, everything must be taken at face value, and if what we take at face value is revealed to be wrong, then there is a paradox. A common skeptical argument consists of equating the realist position on perception with naive realism, and thus concludes that, because such a position is absurd, there cannot be any relation between our perceptions and reality (a position which is called representationalism). But this is a straw man. Sense perception being infallible does not guarantee that we are using rational criteria in evaluating the input of our senses.

Thus this skeptical argument is easily defeated by pointing out the difference between perception and interpretation. In the bent pencil example, the eye correctly transmits the input of light rays that are refracted by the water. But the observer must correctly interpret this input on the basis of a special condition (looking at something in water from a position in air). Thus the necessity of interpreting our perceptions with rational facts is demonstrated.

Skeptics sometimes also use Descartian arguments to attempt to undercut the perceptual basis of the evidence. For instance, they will invoke the possibility that reality as we perceive it is itself an illusion, Matrix-style. True, there is such a possibility. But why should we consider this possibility as having any epistemic importance whatsoever? And of course, to call it any more than a possibility would demand evidence – perceptual evidence.

There are two possibilities: either we will discover evidence for this position later, or we will not. If we don’t, then there is no point in discussing it. If we do find evidence, then the position will be confirmed, and we may have to revise our interpretations to incorporate new rational facts that are derived from it. But in no case does this possibility make sense perception fallible.

Sense perception is also attacked by theologians on the basis that it is incomplete, and that we need to compensate for its lack of capacity to perceive God by using other means. But this is an unacceptable a priori. If we are unable to perceive God in some way, on what grounds can we assume its existence? And even if believers could prove God’s existence – which they cannot – on what grounds can we assume that it could be perceived?

And finally, if everyone perceives God’s existence, as some posit, why are there so many non-Christians? Surely, if God is infinite and perceivable, his existence should be as obvious as the existence of the very Earth. Yet no one denies the existence of the Earth.

More sophisticated theologians have attempted to rest their case on a sensory interpretation of this capacity to perceive God. They posit a divine sense (sensus divinitatis) as our means to perceive God. But this sense falls even the most elementary tests of any sensory means:

  • It has no known organ.
  • It has no evolutionary advantage.
  • It has no known transmission or error-correcting mechanism.
  • It seems very probable that what is actually perceived by this “sense” is part of the imagination, since everyone’s imagination varies (as the perception thru this religious sense also varies from one person to another), and not reality.

    We must conclude that sense perception is infallible and undeniable, and that any attempt to prove otherwise fail.

    Last updated: 01/01/05