The adjective perfect is not applicable to a poem so obscure that more than half its meaning has to be read between the lines, while its plan, if plan it has, is so mixed up and hindmost foremost that I sometimes feel tempted to accept the view of Herder and others that the Song of Songs is not one drama, but a collection of unconnected poems.

And if, "He need not have gone," is a correct expression, need is clearly proved to be an auxiliary, and the three words taken together must form the potential perfect.