A partial reason in favor of something is a consideration that, taken alone, is not sufficient to establish an obligation (even a prima facie obligation), but goes some way toward it. However, it may be the case that several partial considerations taken together could support a full-fledged obligation. As a very simple example, the fact that almost everyone from the department is going to the department’s party might be a partial reason for me to go as well. Taken by itself, that (partial) reason is not enough: were it for that fact only, I wouldn’t have a full-fledged reason to go the party, let’s stipulate.