Plato’s Ingredient Principle: Phaedo 105a2-5

Abstract

In his final argument for the immortality of the soul in the Phaedo, Plato relies on the following principle: Whenever something A enters another thing B and as a result, B comes to be F, A does not admit the opposite of F. This principle seems to be either mistaken or unhelpful. For, on one reading, it says that A itself cannot exhibit the opposite of F, but it seems that in some cases, this is possible. On another reading, it says that as long as A is present in B, B cannot exhibit the opposite of F. For instance, saccharine makes your coffee sweet but is bitter in itself. This, however, would not lead to the desired conclusion that the soul, which brings life to the body, cannot be the opposite of alive. It rather shows that the ensouled body cannot be the opposite of alive. This paper will show that we can accept the first reading, and thus understand why Plato thought that a disembodied soul cannot perish, if we replace the distinction between things and their properties with a slightly different one.