The elements of discourse are what we know and the terms which make up what we know. Before we can take up the three arts, we need a straightforward account of how our words relate to our thoughts and to things.
What a thing is
In the classical tradition, we sometimes speak about things and sometimes about beings. What is the difference? A thing (Latin: res) is anything that we can speak about considered as to what it is, that is, as to its essence. Trees, numbers, colors, laws, and associations of lawyers are all things in this sense. When we consider the same things as to whether they exist, we speak instead of a “being”; so, when we consider tree in general or association in general we are considering tree or association as a thing; when we consider this tree here or this particular association, we are considering them as beings. So the word “thing” is quite general; it covers whatever can be named and considered; and in logic we are concerned with things, not beings. (To be clear, we are not concerned with individuals here and now in logic but with essences and the general characters of things.)
The first operation of the intellect is the grasping of the essence of anything that can be spoken about, that is, the grasping of the essence of a thing (res) as we just defined it.
The concept
When we come to understand something, the mind draws out from our experience what the thing is (the tradition calls this abstraction) and forms within itself a concept of that thing. The concept is the "term" (from the Latin terminus, end) of our act of understanding, that is, the concept is what our act of understanding a thing produces. A concept is also called a “term” in logic because a concept is what stands at each end position of a proposition, namely as subject or predicate in a statement of the form “A is B.” These positions are what define the second act of the mind, the proposition.
Words differ from one language to another, but concepts of the same thing are the same for everyone. English says “cat” where another language might say “billee,” but the concept is one, because both are understandings of the same kind of animal. Compare two photographs of the same thing taken by two people: the cameras differ, but what is shown is the same; this is also true of concepts.
This is a counterintuitive claim in our time, but it is a foundational one for the whole classical tradition. Sometimes two people seem to disagree about a concept when they are really using the same word but using it for two different concepts. If one person means by “faith” a feeling and another means a virtue, they are not yet talking about the same thing. It is true, of course, that one person's concept can be clearer than another person's concept of the same thing, but the central point is that concepts of the same thing are in fact the same. Getting clear on which concept a word carries is part of the first operation of the intellect.
Concepts are likenesses of things and make us aware of the things they are likenesses of. This is how concepts are about things. But note that concepts do not just happen to be about things. It is not as if the concept of cat could somehow be the concept of something else or the concept of cat could somehow be anything other than a concept. In this way, concepts are like our experiences through the senses: if we see something, that act of seeing could not be anything other than an act of seeing. So, a concept, just by the kind of thing it is, is a likeness of the thing that it is a concept of.
The order of words, concepts, and things
When someone speaks to us, their words, which are sounds carried through the air to our ears, bring to our mind the concepts that those words refer to and those concepts immediately bring to mind the things that those concepts are concepts of. If someone says that the piano is black, those words "piano" and "black" bring to our mind the concepts of piano and the color black and through the concepts of piano and black we have now in mind pianos and the color, which are real things. So, do words refer to things or concepts? Words refer to things through concepts, since a word does not refer to a concept first and primarily but to what the concept is a likeness of. Words, therefore, refer ultimately to things but they do so through the concepts of the mind.
This means that words are signs. Just as smoke is a sign of fire, so too a spoken word which is a physical sound is a sign of a concept in the mind and calls that concept to our awareness. So, words are signs of concepts directly and only through concepts are words signs of things.
But what precisely is a sign?
Sources: Aristotle states the order among words, concepts, and things at the opening of On Interpretation, and Aquinas explains it in his commentary (In Peri Hermeneias I, lect. 2).
Continue to Words as Signs.