Human beings are composed of matter and of spirit. This is true even if there is no such thing as spirit (but there is such a "thing", if thingness is correctly understood). To say that man is spiritual is to say that man desires those things that lie beyond the material. What things, you ask? Why, things such as love and truth and beauty, I respond. But all of these things spring from the material, you respond; they are but terms that we apply to our experience of the material. In fact, they are aspects of the human imagination (both collectively and individually) interacting with external stimuli, putting these experiences into the context of a constructed story. Can we live without this story, I ask? No, you respond, it is an extension of the material, but we cannot experience it as such. We cannot treat ourselves as mere complex bio-chemical machines, but must act as though the imaginative story of love and truth and beauty is real, even though it isn't. Ah, I respond, so we have stumbled upon the mystery of human freedom in the face of a predetermined materialism; you must be a reformed theologian. No, you respond, I am a scientist and an atheist. But only in your imagination, I respond. You already believe in spirit, though you don't know it yet.