는다면

If you were to do that

Sets up a hypothetical action — one you are imagining rather than expecting: if I really were dying, if you could only ever eat one food, if you don't bring a special bag, if someone asked me how he looks in person. It leans towards the unreal and the what-if, which is why quiz questions and thought experiments use it. Plain 면 covers ordinary conditions that may well happen; 는다면 signals you are supposing.