Peirce’s sign model is introduced as incompatible with structural semiology in the majority of semiotics textbooks. In this paper, I would like to argue against this general polarization of the semiotic discipline. I focus on compatibilities between Lucien Tesnière’s syntactic theory (verbal valency) and Peirce’s logic of relatives. My main argument is that structural linguistics is not necessarily dyadic, and that Peirce’s sign doctrine is perfectly structural. To define the structural approach in Peirce, I analyze the notions of form (structure) (...) and substance in Hjelmslev and Peirce. The aim of my argument is to contribute to attempts to introduce Peirce’s theory to the field of linguistics in the hope that such an integration will be beneficiary for general linguistics. To extend and support my argument, I provide some examples from biology where Peirce’s theory has been applied. I demonstrate an analogy between the biological structures of proteins and the structure of a sentence with Peirce’s own writings. I consequently introduce Peirce as the first structural semiologist and as the first biolinguist. (shrink)