Rick altman equates a genre's visual conventions with a sentence's ; just as we know that some words don't logically work together, we also sense that a menacing castle doesn't fit in the western.

Semantics.

Explanation:

Semantics cares about the meaning of a word or a sentence. In this case, Altman is equating a genre's visual conventions with sentence's semantics. The effect might be the same: To use different combinations of words or drawings to achieve the desired effect. As Altman says: just as we know that some words don't logically work together, we also sense that a menacing castle doesn't fit in the Western. The example he uses means to find meaning in something that should not be there.