This paper proposes a method for identifying product portfolio architecture alternatives based upon customer needs and product function. Customer needs and uses are interpreted according to the variation in performance target values across the market and within the set of individual customer uses. Product uses are represented by function structures consisting of the functions necessary for achieving the use. These individual product use function structures are combined into a monolithic function structure to represent the entire product portfolio. This monolith is then partitioned according to function and product variety heuristics into function clusters that anticipate product modules. This candidate modularity can then be used to deliver product variety across the product portfolio given functional constraints. A portfolio of xerographic products is used as the working example.