A logical assumption is an assumption that follows sound logic and supporting evidence. It also acknowledges that variables which may make the assumption false do not exist.
An example of a logical assumption is, "The sun will rise tomorrow morning." The sun has always risen, the act of the rising sun is not random, and no known factors may prevent the sun from rising in the near future. However, logical assumptions may still be wrong. For example, if a person were to hear a scratch at his door, it might be perfectly logical to assume it's the cat, although it can be something else.