various arts have been brought about, for any man may fill up a deficiency.
You must remember also what has been already stated, and not seek for exactness in all matters alike, but in each according to the subject-matter, and so far as properly belongs to the system. The carpenter and geometrician, for instance, inquire into the right line in different fashion: the former so far as he wants it for his work, the latter inquires into its nature and properties, because he is concerned with the truth.
So then should one do in other matters, that the incidental matters may not exceed the direct ones.
And again, you must not demand the reason either in all things alike[1], because in some it is sufficient that the fact has been well demonstrated,1098b which is the case with first principles; and the fact is the first step, i.e. starting-point or principle.
And of these first principles some are obtained by induction, some by perception[2], some by a course of habituation, others in other different ways. And we must try to trace up each in their own nature, and take pains to secure their being well defined, because they have great influence on what follows: it is thought, I mean, that the starting-point or principle is more than half the whole matter, and that many of the points of inquiry come simultaneously into view thereby.
VIII
We must now inquire concerning Happiness, not only from our conclusion and the data on which our reasoning proceeds, but likewise from what is commonly said about it: because with what is true all things which really are are in harmony, but with that which is false the true very soon jars.
Now there is a common division of goods into three classes; one being called external, the other two those of the soul and body respectively, and those belonging to the soul we call most properly and specially good. Well, in our definition we assume that the actions and workings of the soul constitute
