DE&E: Chapter 6:6

Let the parade of accidents continue! (And isn’t that a vivid image!)

We should also note that some accidents are caused by the essential principles of a thing according to its perfect act, as heat in fire, which is always hot, while other accidents are the result of an aptitude in the substance, and in such cases the complete accident arises from an exterior agent, as transparency in air, which is completed through an exterior luminescent body. In such things, the aptitude is an inseparable accident, but the complement, which comes from some principle that is beyond the essence of the thing, or that does not enter into the constitution of the thing, is separable, as the ability to be moved, and so on.

So we’ve got the following:

  • Accidents based on the essential principles of a thing:
    • E.g., heat in fire: fire is always hot
  • Accidents resulting from an aptitude in the substance that is completed by some other agent
    • E.g., Air will always let light pass–if there’s light to pass.
    • E.g., an apple is moveable–if I choose to pick it up.

In the latter case, the aptitude is always present–it’s a property of the substance, I guess–but the aptitude is only manifest when some other agent takes advantage of it. For example, a book by Terry Pratchett always has the aptitude to induce laughter, but only does so if you read it.

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