I have finished my discussion of self-evident concepts. Concepts do not do anything except refer to things in our experience. They must be combined in order to be of any use. There are exactly two ways to combine concepts. They may be combined as a definition or as a sentence.

The difference between a definition and a sentence is that a definition is a concept and a sentence is not a concept. All concepts are either self-evident or known by their definitions. A concept must refer to a single thing. If that thing is not self-evident, then we must use our current concepts to give it a name. I do not mean that we must refer to it by a set name to know what it is, but that we could not even recognize it if it was neither self-evident nor known by other concepts. If we were aware of it directly through any of our senses, self-reflection or a combination of those then it would be self-evident. But all concepts are known this way or are built out of concepts that are known this way.

Definitions have two elements. They have a genus and a difference. The genus is what kind of thing the concept is. For example, “white” is a color, humans are animals and 3 feet is a measure. Every defined concept has a genus. A genus is necessary because a defined concept must be a variation of some other concept. The concept that it is a variation of is the genus. The difference is what kind of variation the concept is. If humans are rational animals, then rationality is what makes humans different from other animals. Every defined concept must have a difference. This is necessary because we must know what makes the concept different from other concepts to know what the concept is. Without knowing what the concept is, it cannot be known by definition.

Sentences are similar to definitions. They are unlike them in two respects. First, some sentences are self-evident. Second, sentences are either true or false. Just as all definitions have a genus, so all sentences have a subject. They need a subject because they need something to speak about. Just as all definitions have a difference, so all sentences have a predicate. But the relationship between subject and predicate is different from that of genus and definition. A sentence says that some subject has a predicate added to it (if true) or separated from it (if false). For example, it might say of my chair, that it is wooden. A definition of a wooden chair is different than a sentence that a particular chair is wooden.

Sentences and definitions may both be nested. So the definition of human may be rational animal. But the definition of rational is having a power of reasoning. Both power and reasoning are self-evident concepts gained by self-reflection on one’ s own reasoning and activity. So a fuller understanding of rational animal requires these concepts. Sentences may also be nested. Human beings can walk. Humans is the subject and “beings that can walk” is the predicate. But we can ask why this is so. Doing so will produce two sentences. Humans are mammals, and mammals have the ability to walk because of their morphology (body structure). Those sentences explain why “humans can walk” is true. We can proceed until we reach self-evident truths in both definitions and sentences.

There are a number of objections to this, so I will discuss them next.

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