Robert K. Merton's "distinctions between manifest and latent functions (those consequential activities that are present in the actor's mind and those that are not)" (Coser 567) gives sociological analysis a realistic foundation missing from other analysts' work. Merton's manifest and latent functions allow him to focus on the effects of the actor's mixed motivations, choices, and social constraints: "People . . . are not free to act as they please, but have alternative modes of action. These, however, are structurally patterned and institutionalized" (Coser 566).
Randall Collins writes that Merton's sociological contribution in functional terms is
a two-level inquiry, showing how the surface of our beliefs and actions is determined by a structural basis below. Merton interpreted the structural basis as a tendency of the society to maintain itself. There are manifest functions, which are results that people consciously try to attain, and latent functions, which are produced by the action of the social system itself (Collins 198).
Merton's analysis of latent and manifest functions is crucial to a comprehensive understanding of society and its actors because it refuses to accept surface appearance as reality, and because it also refuses to accept any institution---legitimate or illegitimate---as free from functional influences.
For example, as Collins points out, the "machine politics" of big American cities was so firmly entrenched not simply because it was well-funded and led by powerful if corrupt officials, but because it gave the people something which the "official bureaucracy" could not give, and because, obviously, it served the needs of the corrupt officials themselves. Even more meaningfully, whether or not the that bureaucracy could actually deliver those benefits or services or not, the people believed that it could not, and they made their decisions based on that perception. Collins goes on to apply this Merto...