The Concept of Aspirin Is Not Logically Independent of Its Existence

Jula Klima points out that the lesson we should draw from a breakdown of the substitutivity of identicals depends on whether or not the concepts involved are logically independent. For example, I might know that something is aspirin without knowing that it is currently less popular and analgesic than acetaminophen. But if I have a complete knowledge of the chemical essence of aspirin, I could not fail to know that it is acetyl-salicylic acid. So there's an asymmetry here between the two cases.