form a mental image of something that is not present or that is not the case; "Can you conceive of him as the president?"
If you imagine something, you think about it and your mind forms a picture or idea of it. He could not imagine a more peaceful scene Can you imagine how she must have felt when Mary Brent turned up with me in tow? Imagine you're lying on a beach, listening to the steady rhythm of waves lapping the shore I can't imagine you being unfair to anyone, Leigh
If you imagine that something is the case, you think that it is the case. I imagine you're referring to Jean-Paul Sartre `Was he meeting someone?' --- `I imagine so.' = suppose