In discussions of reasoning or causality, a proximal factor is one that is close to the phenomenon you're studying, as opposed to a distal cause, which is conceptually or temporally distant. You might ask "why is there that stupid node about invisible husbands?" A natural answer would be "because someone thought it would be amusing," but a more proximal cause would be "because there was some text in the writeup box, and the author clicked stubmit."

Proximal causes are very closely related to their effects. As a cause becomes more proximal, it approaches indefeasibility under the laws of physics. However, it also tells us less and less about the larger context or related matters of interest.