We must bear in mind, however, what was said above, and not demand the same degree of accuracy in all branches of study, but in each case so much as the subject-matter admits of and as is proper to that kind of inquiry. The carpenter and the geometer both look for the right angle, but in different ways: the former only wants such an approximation to it as his work requires, but the latter wants to know what constitutes a right angle, or what is its special quality; his aim is to find out the truth. And so in other cases we must follow the same course, lest we spend more time on what is immaterial than on the real business in hand.