Hi, I'm Peter Adamson, and you're listening to the History of Philosophy podcast, brought to you with the support of the Philosophy Department at Kings College London and the LMU in Munich, online at historyofphilosophy.net.

Today's episode, the acid test, theories of matter.

Is a human body more like a cake or more like fruit salad? You might say like a cake because its arrival means that it's somebody's birthday.

But what I mean is something else, I'm asking you about the human's material composition.

If your body is like a cake, then the stuff that was used to make you has been replaced with a new substance.

Just as there are no actual eggs in the finished cake, the initial ingredients of your body are no longer actually present in your body.

This would be the view of Thomas Aquinas, who held that each substance has only one form.

For him, a human body is made ultimately of the four elements, and even they have a material substrate namely formless prime matter.

But the elements and higher level ingredients, like blood or bone, have been taken up into the compound of form and matter that is the body.

All this stuff has literally been transformed, rendered from earth or blood into something new by receiving the form of humanity.

If, by contrast, the human body is like a fruit salad, then it consists of parts that remain the same as they were before they were combined to make the body.

Parts that will also retain their nature is once the body is destroyed.

You can also take parts out of the body without necessarily destroying it by drawing blood for instance or pulling a tooth.

This is like removing the bits of banana that someone unaccountably thought would be nice to include in the fruit salad, forgetting that they always get mushy.

If this is your view, then you think that the substances we see being generated and destroyed, as when people are born and die, are made up of corpuscles, meaning small bodies.

And in the unlikely event that you live in the 16th or 17th century, if you believe in corpuscles, then you are probably an atomist, meaning that for you, the human body and indeed every physical object is an aggregate of indivisible particles.

But you don't actually need to believe that the parts are literally atoms, that is uncutables, which is what the Greek Atomam means, as I mentioned, 380 episodes ago, when covering the ancient atomists, democratists and neocupis.

Maybe the corpuscles are in principle divisible, maybe they aren't.

Sometimes scientists at this period casually refer to things as atoms, just to mean that they couldn't be divided through any known laboratory technique.

They might even be visible, as in a vapor cloud that is made of tiny droplets or metal that has been turned into a pile of so-called atomic powder.

The real point is that they are actually present in the substance, all jumbled together to constitute, in the case of the human, blood, bone and ultimately the whole body.

To find out whether a substance is like cake or like fruit salad, a good test would be whether you can decompose the substance into the same ingredients you used to make it in the first place.

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