This talk will offer an overview of a current understanding of the content and the form of linguistic roots. It first reviews the cases i) against semantic content of uncategorised roots and ii) for Late Insertion of roots; then it investigates how native speakers identify roots. First, the idea that roots may be polysemous or may encode the shadow of a denotation is refuted. Second, the existence of a spectrum of content to which roots belong, with roots ranging from contentless to semantically specific and concrete, is also shown to be illusory, and to result from the actual productivity of the words derived from them. Harley’s arguments for Late Insertion of roots are then reviewed and updated, divorcing roots from the forms that realise them. These points are systematically combined with Acquaviva’s analysis of roots as abstract indices, i.e. as the syntax-internal criteria of lexical identity. Finally the approach at hand is taken to its logical conclusion: if roots are indeed abstract indices, then they cannot be identified either by the semantic content they realise within grammatical structures or by their forms. Roots are hence identified just once by native speakers over their lexicon at a given moment and on the basis of three heuristic principles: one form-based, one based on the feature content and the exponence of the structures in which roots are embedded, and one taking care of root suppletion.