According to Aristotle, when you look at a thing, you see what it is. When you look at a dog, you see that it’s a dog. When you look at a cat, you see that it’s a cat. When you look at a table, you see that it’s a table. He calls this “apprehending the essence of the thing”. “Apprehend” is an interesting word; it means “to sieze”, as opposed to “comprehend”, which means “to grasp”.

So Aristotle isn’t saying that when you look at a dog, you understand fully and completely what it is that makes a dog a dog. He’s simply saying that when you look at a dog, you know it’s a dog, rather than, say, a cat. Even tiny children can tell the difference at a glance.

According to Aristotle, this is simply how our minds work. The dog has an essence, which is simply to say that there is a kind of thing called a dog, that has the nature of being a dog. Your senses perceive the dog, and from the images produced by your senses (which includes the smell of wet dog, the feel of fur, the sound of barking) your intellect abstracts the essence and presents it to you. You don’t need to analyze the appearance of the dog; you just look at it, and know, hey, that’s a dog!

In our modern world, where we tend to think of everything in terms of software and computation, we tend to think, “Oh, I see the dog, and then some pattern recognition software runs in my brain—and very quickly, too!—and it recognizes the pattern of characteristics that makes a dog a dog, and I say, ‘Oh, there’s a dog!'” But according to Aristotle, it’s really simpler than that. The dog has an essence, which is a metaphysical reality; and our intellects are equipped to apprehend that reality, to abstract Dogginess from the Dog that stands before us.

And our intellect saves that essence for later, so we can recognize the next dog we see. Essences are “intelligible”; we can know them directly.

I’ve been reading a book called The Structure of Objects, by Kathrin Koslicki; it’s an attempt, so far as I can tell, to pull some Aristotelian concepts into modern analytic philosophy, about which more later. But only some concepts. She can’t quite bring herself to believe that essences are real, so she resorts to the more modern conception of “natural kinds”; and “natural kinds” are defined, more or less, as clusters of properties that objects of the kind have. According to Koslicki, we recognize a dog because it has floppy ears and a waggy tail and an elongated furry body like a golden retriever or (ahem) a pit bull. Oh, wait, that doesn’t work.

Great Danes and Toy Poodles look rather different, and one could be excused for thinking of them as different species, based purely on surface features. And yet both are known to be dogs. One could appeal to genetics, to numbers of chromosomes and lineages to say, oh yes, these are both dogs; but then we are getting past characteristics that are easily apprehended. In short, appeals to science don’t explain how a two-year-old can look at a Great Dane and a Toy Poodle and recognize them both as fundamentally the same kind of thing.

To be fair to Koslicki, I’m seriously over-simplifying her position, but it doesn’t invalidate my point: essences are something that can be apprehended, seized in a moment without any deep analysis. Koslicki’s position requires a fair degree of comprehension before the objects around us can be grouped into kinds; and that’s nonsense.

And so, as Aristotle says, essences—universals, as they are sometimes called—have a real existence, and our minds are equipped to know them.