It may safely be said that every one who has had to do with technical Arabic has had difficulty with wahm and its cognates. Some recent investigations have led me to examine the meanings of these in detail and I endeavour in this paper to give my results. It will be understood that this is not a complete lexicographical handling of the whole root, but only an attempt to discover the more technical uses of some of its phases. In the arrangement of the material I fear that I have not always avoided logical cross-division; but the subject is complicated and will call for reading backward as well as forward. Also I make no attempt to trace the origin of these Arabic psychological conceptions, whether in Greek, Syriac, or elsewhere, or to compare them with any parallel conceptions in modern psychology. Such few references as I may make, of the one kind or the other, are simply to illumine wahm itself.