In this paper we examine the following problems: How many concepts of funct
ion are there in biology, social science, and technology? Are they logicall
y related and if so, how? Which of these function concepts effect a functio
nal explanation as opposed to a mere functional account? What are the conse
quences of a pluralist view of functions for functionalism? We submit that
there are five concepts of Function in biology, which are logically related
in a particular way, and six function concepts in social science and techn
ology. Only two of them may help effect a genuine functional explanation. F
inally, our synthetic approach allows us to distinguish Four different vari
eties of functionalism in biology, psychology, social science, and technolo
gy: formalist, black boxist, adaptationist, and teleological. And only one
of them is explanatory in the strong sense defended here.