At no moment in time is one free from the information of the senses, or the impressions of such experience. Memory and various habits of mind are, understood from a certain point of view, the residue of perception. Yet, it appears an open question whether perception is knowledge, as Theaetetus claimed in Plato’s eponymous dialogue. Perhaps perception is a mere precursor to knowledge. Perhaps it is the raw material of knowledge.
Aristotle’s philosophy is typically understood as, at least in part, a reaction to that of Plato, his teacher. Plato held that perception was neither knowledge nor (in any straightforward sense) the raw material of knowledge. Rather, he held that it was misleading. Aristotle, in contrast, did not deny perception a role in knowledge. Indeed, he is often understood to have given it a premium place in the theory of knowledge – in other words, to have been empiricist. This article begins by considering that understanding of Aristotle’s work, and simultaneously demanding clarity over the term empiricism. It then moves on to consider if and how Aristotle bases a theory of knowledge on perception. It concludes with a discussion of skepticism about perception knowledge, and whether skeptical objections of this kind have intellectual merit.
Aristotle, the Empiricist
Aristotle is generally agreed to be an empiricist. But what is empiricism? When one talks about empiricism outside of a philosophical context, it is generally in relation to science. Specifically, empiricism is regularly presented as the method of science, or alternatively as the basis on which the claims of science are justified. Common to various theories of science is a two-part conception, which holds that science has a speculative and theoretical element (the thesis), and an empirical and experimental component (the proof).
One of the appeals of this picture is that it appears to exclude various things we do not want to call sciences. For instance, it is often used to mark various points in intellectual history when people stopped merely observing how nature is, and started to theorize about it (in particular, started to theorize causally). However, it’s not difficult to complicate this picture. If we wished to test it thoroughly, we might claim that any activity which does not have both elements is not a science. However, certain attempts to make sense of things which are so large or so distant (or, in the case of astronomy, both) that they cannot be experimented upon require us to limit ourselves to observation without experimentation, or experimentation only with analogous bodies.
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It is in a philosophical context that one begins to discuss empiricism as a theory of knowledge in general. There are various ways in which one might put such an idea. Generally, empiricism stands in for ‘having to do with or putting to use perception’. One might say that our perceptions are the basis of knowledge – that it justifies our beliefs. One might say that it is how our concepts are derived – it is the basis not just of beliefs, but of thought in general. This is where empiricism starts to move away from a theory of knowledge to an ontological stance – that is, a theory not just of how we know what we know, but of the ‘being’ of things (roughly, what there is rather than how we know what there is).
Jonathan Barnes, a contemporary scholar of Ancient Greek philosophy, puts Aristotle’s view succinctly: “Aristotle’s primary research tool was sense-perception, his own or that of others; as an ontologist, Aristotle’s primary substances were ordinary perceptible objects. Plato, having given abstract Forms the leading role in his ontology, was led to regard the intellect rather than perception as the searchlight which illuminated reality. Aristotle, placing sensible particulars at the center of the stage, took sense- perception as his torch.”
This quote raises several questions that are worth addressing clearly. Firstly, what is a ‘sensible-particular’? It is a term that comes from Plato, and simply refers to objects as we experience them using our senses. This leads naturally to the second question: what is the significance of the contrast between Aristotle and Plato?
Plato and Aristotle are generally understood to be philosophical rivals, with opposing theories of the world. Where Plato took sensible-particulars to be shallow, superficial and illusory, Aristotle took them as basic to our ability to make sense of things. It is important to clarify that, although Aristotle takes the sensible-particulars to be the raw material of knowledge, they are not the finished product. Consider the following passage from Aristotle:
“All animals . . . have an innate capacity to make discriminations, which is called perception; and if perception is present in them, in some animals the percept is retained and in others it is not. Now for those in which it is not retained . . . there is no knowledge outside perception. But for some perceivers it is possible to hold the percept in their minds; and when many such things have come about there is a further difference, and some animals, from the retention of such things, come to possess a general account, while others do not. Thus from perception there comes memory, as we call it; and from memory (when it occurs often in connection with the same thing) experience – for memories that are many in number form a single experience; and from experience, or from the whole universal that has come to rest in the mind, . . . there comes a principle of skill and of knowledge.”
Aristotle holds that, whilst all animals perceive, not all animals know and act decisively according to principles (certainly not in the way which human beings know and act).
Aristotle is also making a number of moves in this passage which preempt those which later empiricist philosophers will make. For one thing, he understands memory to be a kind of residue of perception, and represents them as qualitatively similar. For another, he presents similarity in experience – principles of association and resemblance – as the element by which perceptions become principles of ‘skill and knowledge’. In other words, Aristotle locates the formation of concepts which do not themselves appear intrinsically empirical in repetition.
To put the same point another way, knowledge is the compression of memories into a single atom of thought, into a concept. Notoriously, Aristotle doesn’t go to great lengths to defend this theory, in spite of the various plausible objections. He is particularly dismissive towards skepticism of experience as a basis for knowledge:
“It is evident that no one – neither those who state the thesis nor anyone else – is actually in that condition. For why does anyone walk to Megara [a town in Greece] rather than stay where he is when he thinks he should walk there? Why doesn’t he walk into a well or over a cliff in the morning if there is one about?”.
Aristotle on Common Sense and the Practical Sciences
This style of argument appears to precede a whole range of later attempts at arguments from something like ‘common sense’. This argument also seems indicative of the motivation behind Aristotle’s empiricism as a whole. Aristotle wasn’t just a theorist, but a committed practical scientist and collector. Unlike most contemporary philosophers, his concern was not exclusively with making the most elegant argument and then defending it to the hilt.
Aristotle was simply less interested in dealing with certain challenges to his theory, when those challenges ran against both common sense and the method which he had put to such good effect in the realm of natural science.
There is a certain power to this kind of dismissiveness. Even philosophers with no scientific background are sometimes tempted to appeal to a similar kind of practical necessity as a kind of trump card. And clearly there is a kind of thoroughgoing skepticism which has no place in philosophical discourse which aspires to anything productive. All arguments have to come to rest somewhere. And yet, it is not as though these skeptical objections cannot present a serious problem for empiricism. It is not at all the same thing to say that the knowledge of our senses is practically useful as it is to say that it forms a secure basis for knowledge as such.
Indeed, one of the great empiricist philosophers – Scottish David Hume – arguably heralded in modern philosophy by observing that experience alone gives us no basis for believing that truths and practices acquired by our senses are stable, given that the only warrant for such a belief in turn relies on these very senses!