"Yeah, what he said..."

The potentially confusing statement that "evolution is both a theory and a fact" is often seen in biological literature. This statement arises because "evolution" is used in two ways. First, the "fact of evolution" refers to the observed changes in populations of organisms over time, which are known to have occurred. Second, the "theory of evolution" refers to the modern evolutionary synthesis, which is the current scientific explanation of how these changes occur.

On its own, the word "evolution" often refers to the combination of the underlying facts, and the theory that explains them. However, it is also frequently used to refer to one or the other. Readers should take care to determine an author's meaning.

- Wikipedia, Evolution as theory and fact