[First things by nature] [are] the principles, but ultimate things by nature [are] the things far removed from the principles.[1] And these problems are difficult for those who are attempting to prove them, but for those who are answering [they are] easy. For the first things contain what is difficult, because it is not possible to prove them through other things, due to the fact that what is proved is proved through first things, and there is nothing prior to what is first. For knowledge of principles does not come about through demonstration, but through definition.[2] For it is necessary first to define the principle, [i.e.] what it is, and by supposing that the principle is this [i.e. first], to make use of the principle for the proof coming about after the principle. For this reason principles are hard to deal with and not easy to prove. But the ultimate things [sc. are so called] because they are proved through many intermediates. A figure is mentioned 'first' in references to deductive arguments,[3] not as a cause or even as generative of them, but due to arrangement; and [a figure] is more perfect not on account of producing those things or implying [them], but because of being more able to be the most suited to demonstrative methods.