Towards a model of host-parasite relationships

The question asked in this article is: "what is a parasite?". Defining a parasite requires defining its host at the same time. A difficult question therefore arises about host-parasite relationships. The object of general parasitology is in fact to study the relationship between a host and its parasite. The initial question "what is a parasite?" has to be reformulated within a conceptual framework, that of "relationship". This article is an attempt to transpose into parasitology some concepts which have been profitable in the fields of physics and chemistry. The studies of R. Thom about the individual are also used. Concepts like that of field and principles like that of minimization are probably operational on a high level of organization. The description of host-parasite relationships could benefit from these concepts.