Aristotle wanted to do a thorough clearing up in nature's "room." He tried to show that everything in nature belongs to different categories and subcategories. (Hermes is a live creature, more specifically an animal, more specifically a vertebrate, more specifically a mammal, more specifically a dog, more specifically a Labrador, more specifically a male Labrador.)
Go into your room, Sophie. Pick up something, anything, from the floor. Whatever you take, you will find that what you are holding belongs to a higher category The day you see something you are unable to classify you will get a shock. If, for example, you discover a small whatsit, and you can't really say whether it is animal, vegetable, or mineral--I don't think you would dare touch it.
Saying animal, vegetable, and mineral reminds me of that party game where the victim is sent outside the room, and when he comes in again he has to guess what everyone else is thinking of. Everyone has agreed to think of Fluffy, the cat, which at the moment is in the neighbor's garden. The victim comes in and begins to guess. The others must only answer "yes" or "no." If the victim is a good Aristotelian--and therefore no victim--the game could go pretty much as follows:
Is it concrete? (Yes!) Mineral? (No!) Is it alive? (Yes!) Vegetable? (No!) Animal? (Yes!) Is it a bird? (No!) Is it a mammal? (Yes!) Is it the whole animal? (Yes!) Is it a cat? (Yes!) Is it Fluffy? (Yeah! Laughter. . .)
So Aristotle invented that game. We ought to give Plato the credit for having invented hide-and-seek. Democritus has already been credited with having invented Lego.
Aristotle was a meticulous organizer who set out to clarify our concepts. In fact, he founded the science of Logic. He demonstrated a number of laws governing conclusions or proofs that were valid. One example will suffice. If I first establish that "all living creatures are mortal" (first premise), and then establish that "Hermes is a living creature" (second premise), I can then elegantly conclude that "Hermes is mortal."
The example demonstrates that Aristotle's logic was based on the correlation of terms, in this case "living creature" and "mortal." Even though one has to admit that the above conclusion is 100% valid, we may also add that it hardly tells us anything new. We already knew that Hermes was "mortal." (He is a "dog" and all dogs are "living creatures"--which are "mortal," unlike the rock of Mount Everest.) Certainly we knew that, Sophie. But the relationship between classes of things is not always so obvious. From time to time it can be necessary to clarify our concepts.
For example: Is it really possible that tiny little baby mice suckle just like lambs and piglets? Mice certainly do not lay eggs. (When did I last see a mouse's egg?) So they give birth to live young--just like pigs and sheep. But we call animals that bear live young mammals--and mammals are animals that feed on their mother's milk. So--we got there. We had the answer inside us but we had to think it through. We forgot for the moment that mice really do suckle from their mother. Perhaps it was because we have never seen a baby mouse being suckled, for the simple reason that mice are rather shy of humans when they suckle their young.
Nature's Scale
When Aristotle "clears up" in life, he first of all points out that everything in the natural world can be divided into two main categories. On the one hand there are nonliving things, such as stones, drops of water, or clumps of soil. These things have no potentiality for change. According to Aristotle, nonliving things can only change through external influence. Only living things have the potentiality for change.
Aristotle divides "living things" into two different categories. One comprises plants, and the other creatures. Finally, these "creatures" can also be divided into two subcategories, namely animals and humans.
You have to admit that Aristotle's categories are clear and simple. There is a decisive difference between a living and a nonliving thing, for example a rose and a stone, just as there is a decisive difference between a plant and an animal, for example a rose and a horse. I would also claim that there definitely is a difference between a horse and a man. But what exactly does this difference consist of?