Logic is a branch of philosophy, it teaches us to know the truth. The truth is reality, that is, what it is.
The Sun exists: this is a real truth regarding the thing; I know that the Sun exists: this is a formal truth regarding understanding. Knowledge is worthless if it lacks truth, and natural logic is the disposition that Nature has given us to know the truth.
Source
This disposition can be perfected with rules based on reason and experience. There are rules to direct understanding to knowledge of the truth, and there are principles on which the rules are founded. We say that there is logic, that this or that is logical, when we refer to something that fits perfectly within the truth, of reality. An illogical thing is an absurd thing, contrary to the truth. The rules that direct the understanding to true knowledge and the principles on which these rules are based constitute logic.
Source
Insofar as it prescribes the rules, it is art; insofar as it indicates the reason for the rules, it is science. For example: art prescribes the qualities of a good definition, and science indicates the reason for those prescribed in the rule. Art is properly a set of rules to do something well. Having traced this path, which is a set of rules, we will have logic as art.
Source
The understanding is not a blind faculty: when it follows a path, it knows, or at least it can know, why it is following it, and it is capable of pointing out the reason for the rules it observes to arrive at the knowledge of the truth. 《This is how logical science creates》.
Aristoteles was the founder of this philosophical science. His book bears the expressive title of "Organon" = organ, that is to say, instrument; for being it of the safe and straight human thinking.
