There is a marked discontinuity between the principal features of the varieties of logic that were predominant in roughly the first half of the century and the way of viewing logic that came to the fore in the second half. The first half of the seventeenth century may be characterised by a general tendency to continue teaching logic in one of the versions that had been handed down from the remote or near past. As a rule, seventeenth-century textbooks of logic have three main parts: one dealing with concepts or terms as elements of propositions; another discussing various types of mental, spoken, and written declarative sentences or propositions; and a third part in which reasonings as peculiar combinations of propositions were treated. The first part of a textbook of logic was commonly devoted to the smallest relevant units that constitute a proposition. A categorical proposition contains a subject-term and a predicate-term.