Is a man by his words not an assertive sentence?

You're right, the sentence "A man is by his words" isn't an assertive sentence. It's actually a fragment. Here's why:

* Incomplete thought: It doesn't express a complete thought or idea. It needs more information to make sense.

* Missing verb: It lacks a finite verb (a verb that shows tense and agrees with the subject).

* No clear assertion: It doesn't make a definitive statement or claim about a man's character.

To turn this into an assertive sentence, you could add a verb and complete the thought:

* "A man is judged by his words." (This is now an assertive sentence because it makes a statement about how a man is evaluated.)

* "A man is defined by his words." (This sentence asserts that a man's words determine his character.)

Let me know if you have any more sentences you'd like to analyze!