Posterior Analytics (Bouchier)/Book I/Chapter XIV

Chapter XIV: The figure proper to Demonstrate Syllogism

 * The first figure of the syllogism is the most scientific, being the most suitable for the attainment of the cause. Further it alone can examine into the simple fact which must be both affirmative and universal. The other two figures reinforce their demonstrations by an appeal to the first figure, the latter never makes use of them.

Of the figures of the syllogism the most proper for scientific demonstration is the first, for mathematical sciences, such as arithmetic, geometry and optics, and generally speaking all sciences which investigate the cause of things, effect their demonstration by its means. The demonstration of the cause is in fact carried out either exclusively or generally and in most cases by means of this figure, so that in this respect also it appears to be the most proper for science, seeing that the examination of the cause is the most important element in knowing. Further, the knowledge of what a thing is can only be attained by means of this figure, for in the second figure no affirmative conclusion is produced, and the knowledge of what a thing is involves affirmation. In the third figure there are indeed affirmative conclusions, but not universal ones, and the knowledge of what a thing is is of the character of a universal; thus, ‘two-footed’ is true of man universally and without restriction. Moreover the first figure has no need of the assistance of the two other figures, while these latter are strengthened and extended by means of the first until they arrive at ultimate principles. It is clear then that the first figure is the most important instrument of scientific knowledge.