The universal premise states the connection between one of the terms in the conclusion and the middle term. So, the four causes are the four general kinds of grounds or reasons that can establish a connection between the subject and predicate terms of any conclusion. In other words, if you took every argument, expressed each argument in valid syllogistic form, you would be able to categorize the relationship between each middle term and the other terms as belonging to one of these four categories of reasons. Mammal is the genus of whale. When you give a definition of what a whale is, you identify whales as belonging to the class of mammals.
All paper burns.
Tom has big biceps. All professors wear leather elbow patches on their tweed sport jackets. The connection is a matter of purpose. The professor wears leather elbow patches with the aim of looking cool. Thus, the doctrine of the four causes is a way of categorizing and labeling the kind of reasons we give for connections we make whenever we draw conclusions.