In “The Marriage of Heaven and Hell,” Blake grapples with the problem of vision.  Much of this work is about looking at the world in a different way in order to achieve poetic genius and to explore contraries, which are “necessary to Human Existence”.  The problem with achieving this vision is that one’s sense of sight is limited, or we are taught to think that our sight is limited.  The Devil stresses this dilemma when he says, “How do you know but ev’ry Bird that cuts the airy way,/ Is an immense world of delight, clos’d by your senses five?” (71)  There is a problem of perception here.  We see a bird and think it is only a bird, but that is because we are limited by our five senses.  If we could open ourselves up to a sort of sixth sense, we would see that this bird actually contains many more possibilities beyond what we originally thought.  So what’s the sixth sense that allows us to do this?  Blake’s answer is two-fold:  the poetic imagination and the constant questioning of both, contrary sides of any situation.  Blake says “If the doors of perception were cleansed every thing would appear to man as it is, infinite.  For man has closed himself up, till he sees all things thro’ narrow chinks of his cavern” (75).  Blake argues that man needs to open himself up to different ways of seeing the world.  Man broadens his perspective through the questioning of contraries.  In the opening pages of analysis before the poem, Blake’s narrator is referred to as a “young contrarian who breaks out of the limits of this world” (67).   The way to expand your vision is to question and explore contraries.  Through this process of exploration, you will employ your imagination and perhaps discover your own poetic genius.