A premise is something that is a previous statement or proposition from which another is inferred or follows as a conclusion. if the premise is true, then the conclusion must be true Something to base an argument, theory, or undertaking on. The basis, or the idea being proposed or expounded.
In The Oath of the Horatii, the main message David wishes to communicate is that of men going to battle for the sake of loyalty, with possible sacrifice. There are several signs that allow the viewer to read this narrative, then further associate it with the ancient story from which the image was born.
An oath of fealty, from the Latin fidelitas (faithfulness), is a pledge of allegiance of one person to another.