Kitap 7
1.75
Again, some things are possible, others impossible; and some things are necessary, others are not necessary. A proposition is possible which admits of being true, there being nothing in external circumstances to prevent it being true, e.g. Diocles is alive. Impossible is one which does not admit of being true, as e.g. The earth flies. That is necessary which besides being true does not admit of being false or, while it may admit of being false, is prevented from being false by circumstances external to itself, as Virtue is beneficial. Not necessary is that which, while true, yet is capable of being false if there are no external conditions to prevent, e.g. Dion is walking.
1.76
A reasonable proposition is one which has to start with more chances of being true than not, e.g. I shall be alive to-morrow.
1.76
And there are other shades of difference in propositions and grades of transition from true to false— and conversions of their terms—which we now go on to describe broadly.
1.76
An argument, according to the followers of Crinis, consists of a major premiss, a minor premiss, and a conclusion, such as for example this: If it is day, it is light; but it is day, therefore it is light. Here the sentence If it is day, it is light is the major premiss, the clause it is day is the minor premiss, and therefore it is light is the conclusion. A mood is a sort of outline of an argument, like the following: If the first, then the second; but the first is, therefore the second is.
1.77
Symbolical argument is a combination of full argument and mood; e.g. If Plato is alive, he breathes; but the first is true, therefore the second is true. This mode of argument was introduced in order that when dealing with long complex arguments we should not have to repeat the minor premiss, if it be long, and then state the conclusion, but may arrive at the conclusion as concisely as possible: if A, then B.
