This dissertation is a study of the construction of meaning below the word level, specifically how roots and morphemes combine to create verbs, and the contribution of each to the meaning that a verb construes. It uses data from the verb system of Modern Standard Arabic to bring together the theory that roots combine with different structures to produce verbs describing different types of event, and the observation that many roots cannot form verbs on their own, and must combine with other morphemes do to so. The thesis is that Arabic roots lexicalize events, states or things, but remain free to create new meaning in combination with the different verb stems of Arabic, each of which contains one or more morphemes that determine the type of event that a root may come to describe. The findings are that the morphemes present in the different verb stems of Arabic condition verb meaning in four main ways: through reflexivization; through providing an Actor subject argument; through marking plural event phases; and through marking the presence of two relations construed as one event. A root combines with a morpheme that determines the type of event that a verb may describe, and it contributes meaning within the limits set by that morpheme. Thus morphemes do not modify a fixed concept, but root and morpheme create verb meaning together. The implication of this for a theory of meaning below the word level is that the semantic concepts which humans communicate remain relatively constant, but they are expressed at different levels of granularity: at the root level; by combining roots below the word level; by combining roots with morphemes below the word level; and by combining words at the clause level. This opens up avenues for further research to establish the differences, if any, between the meanings construed at these different levels of granularity. / text