very thing which occasions the doubt is to be referred; for the mode being evident, it is clear that it will be necessary, either to define, or to divide, or to prepare middle propositions, since through these, the last are demonstrated.
In many theses also, when the definition is not well delivered, it is not easy to discourse and argue, as whether one thing is contrary to one or many things, but contraries being defined properly, we can easily collect whether there can be possibly many contraries of the same thing or not. In the same way also, as to other things which require definition, and in mathematics, some appear not easily described through a defect of definition, as that a line which laterally cuts a superficies divides similarly both a line and a space. When, however, the definition is stated, the assertion is forthwith evident, for both the spaces and the lines have a correspondent division, but this is the definition of the same sentence. In short, the first elements when definitions are laid down, as what is a line, and what a circle, are easy of demonstration, except that we cannot advance many arguments against each of these, from there not being many media, but if the definitions of the principles be not laid down, it is difficult, and perhaps altogether impossible; likewise also in those, which belong to disputations.
It ought not, therefore, to escape us, that when a thesis is opposed with difficulty, it has experienced some one of the above-mentioned (modes); since, however, it is more difficult to discuss an axiom and a proposition than a thesis, a person may doubt whether things of this kind are to be laid down or not. For if he does not admit them, but thinks fit to discuss this also, he will enjoin a greater work than what was at first laid down, but if he does admit, he will
