Question

Although the words “mentioned” and “declared” have similar meanings, they are different because _____.

Answer 1

They are different because they have distinct denotations. Denotations give the literal meaning of the word. According to macmillan dictionary, “mentioned”  refer to something briefly without going into detail and “declared” means saying something in an empathic manner. 

Answer 2

Mentioned is to refer to something briefly and without going into detail. "I haven't mentioned it to William yet" While Declared is to say something in a solemn and emphatic manner. "he declared that he never revises his prose"