What does "inconsistent" mean?

Inconsistent: Not exhibiting uniformity of sentiment, steadiness to principle, etc.; unequal; fickle; changeable. Ah, how unjust to nature, and himself, Is thoughtless, thankless, inconsistent man. Young. -- Inconsistent, Incongruous, Incompatible. Things are incongruous when they are not suited to each other, so that their union is unbecoming; inconsistent when they are opposed to each other, so as render it improper or wrong; incompatible when they can not coexist, and it is therefore impossible to unite them. Habitual levity of mind is incongruous with the profession of a clergyman; it is inconsistent with his ordination vows; it is incompatible with his permanent usefulness. Incongruity attaches to the modes and qualities of things; incompatibility attaches to their essential attributes; inconsistency attaches to the actions, sentiments, etc., of men.