The Posterior Analytics is concerned to provide an account of scientia or “scientific knowledge.” By this is meant not scientific knowledge in the modern sense of a body of theory based on the experimental testing of hypotheses, but rather an understanding of the reason why a given fact obtains (knowledge propter quid), as opposed to knowledge simply that the fact does obtain (knowledge quia), what might be described as a certain kind of explanatory knowledge. An Aristotelian science is a systematization of such knowledge based on the structure of Euclid’s axiomatic geometry and employing Aristotle’s syllogistic logic. One arrives at scientia of a given fact by deriving it as the conclusion of a syllogism whose premises meets certain stringent conditions that render them explanatory of that fact. As Grosseteste puts it, the premises or principles–i.e., starting points–of such a syllogism must be true, immediate, prior and better known than the conclusion, must state causes, be necessary, concern essential connections, be universal, everlasting, and incorruptible. A syllogism that meets these conditions is called a demonstrative syllogism or demonstration and will provide explanatory knowledge of its conclusion. At one point Grosseteste states that only mathematics is comprised of demonstrations in this strict sense, though in another passage he suggests that theology would most fully meet these conditions, apparently meaning that the demonstrative knowledge possible for us in this life (mathematics) is to be distinguished from that which is possible in the afterlife (theology). The sciences of natural phenomena do not, Grosseteste claims, fully meet the requirements for a fully demonstrative science, though if we relax the conditions governing demonstrations somewhat we may speak of a demonstrative science of natural phenomena (see the entry on Medieval Theories of Demonstration for details).