According to the traditional interpretation of Aristotle there is a plurality of numerically distinct, but essentially identical particular forms in the external world, and what is ´common´ to these particulars is o n e universal form, knowable to the human mind. Hence form is an ontological as well as an epistemological concept. By and large, this view is certainly correct, but it has been intensely discussed whether it implies that form ´in itself´ is particular or universal.
The present study argues that this question is a ´category mistake´. A form is not a ´something in itself´ - it is a structure or principle of one or many ´things´. A structure is not a thing, and intension precedes extension - which could explain why Aristotle himself never explicitly defines form as particular o r universal. In his detailed argumentation he often attacks what he takes to be the Platonic position vehemently. But in a postscript to this study it is claimed that deep similarities connect the two essentialists, Plato and Aristotle - the Aristotelian view should be seen as an innovation within a Platonic frame.