My book says that matter can be classified as an element, compound, or mixture. It further says that a pure substance (or substance) is matter that has distinct properties and a composition that doesn't very from sample to sample. So far, so good. Then it says that
all substances are either elements or compounds
An element is one type of atom (something that "cannot be decomposed into simpler substances") and a compound is composed of two or more elements; these both clearly are substances. Then, it says that
Mixtures are combinations of two or more substances in which each substance retains its chemical identity.
This is where I'm confused. How are mixtures not substances? They have distinct properties, and their composition doesn't vary from sample to sample, if you set a standard for the sample. You can create any arbitrary mixture, and you can create any arbitrary compound, and if you follow the "recipe" for either you will always get the same thing, as far as I know.
Where is my logic flawed?