“If the lamp is on, the room will be illuminated” is a conditional. We need not establish that the lamp is currently on in order to understand the claim; the main issue is the asserted connection between illumination and a lit lamp.
Even when the lamp is off, we can grasp the conditional's meaning and discuss whether the stated relation holds.
Thus hearing the antecedent in a conditional is not the same as asserting that it is actual. This distinction later matters in conditional reasoning and inference.