Words in fluent speech frequently differ from their citation forms. This paper investigates some factors influencing the realization of the preposition for and the number four. Realizations of these words in read and spontaneous speech show that instead of viewing function words as having discrete weak, strong, or even intermediate allomorphs, a continuum resulting from gestural interaction better represents the facts. In the speech examined here, numerous factors influence different aspects of the realization of for and four. The duration of the onset /f/ is affected by the preceding prosodic boundary while the duration and composition of the rime is affected by foot structure and segmental content. The preposition exhibits extreme reduction possibilities not seen in the number. In even this small set of studies, the read and spontaneous speech highlight different generalizations, pointing out the need to examine both kinds of speech. While this paper cannot locate all factors responsible for the variation in these words, it begins to unravel some of them and their effects on different portions of function words.