When a man says that he grasps an argument he is using a verb (grasp) which literally means to take something in the hands, but he is certainly not thinking that his mind has hands or that an argument can be seized like a gun. To avoid the word grasp he may change the form of expression and say, ‘I see your point,’ but he does not mean that a pointed object has appeared in his visual field. He may have a third shot and say, ‘I follow you,’ but he does not mean that he is walking behind you along a road. Everyone is familiar with this linguistic phenomenon and the grammarians call it metaphor. But it is a serious mistake to think that metaphor is an optional thing which poets and orators may put into their work as a decoration and plain speakers can do without. The truth is that if we are going to talk at all about things which are not perceived by the senses, we are forced to use language metaphorically. Books on psychology or economics or politics are as continuously metaphorical as books of poetry or devotion. There is no other way of talking, as every philologist is aware.