Three aspects of logic should not be treated as interchangeable.
Definition: A science whose rules, when observed, protect the mind from error in thought.
Subject matter: Known concepts and judgments considered insofar as they lead to unknown concepts and judgments.
Aim: To attain correctness in thinking and avoid errors of inference.
These respectively describe what kind of discipline it is, what it investigates, and what benefit it seeks. Its field of inquiry and its purpose are connected but not synonymous.