An argument is:

A set of one or more propositions (or claims), called premises, advanced as proof or evidence for another proposition, called the conclusion.

A cogent (or good) argument must meet three conditions. If any of the conditions is not met, the argument is fallacious:

(a) the reasoner(s) must be warranted in believing the premises

(b) the argument must proceed according to a correct principle of reasoning

(c) one must argue in good faith and not suppress relevant evidence.

If these three conditions are met, one is warranted, or justified, in believing the argument's conclusion.

N.B. Argument layeredness.