Aristotle - The Organon - index for DE INTERPRETATIONE Book 1 Part 13

Possibility and contingency

Paragraph 1 Logical sequences follow in due course when we have arranged the propositions thus.
Paragraph 2 From the proposition 'it may not be' or 'it is contingent that it should not be' it follows that it is not necessary that it should not be and that it is not impossible that it should not be.
Paragraph 3 Let us consider these statements by the help of a table:
Paragraph 4 Now the propositions 'it is impossible that it should be' and 'it is not impossible that it should be' are consequent upon the propositions 'it may be', 'it is contingent', and 'it cannot be', 'it is not contingent', the contradictories upon the contradictories.
Paragraph 5 We must investigate the relation subsisting between these propositions and those which predicate necessity.
Paragraph 6 Yet perhaps it is impossible that the contradictory propositions predicating necessity should be thus arranged.
Paragraph 7 Yet from the proposition 'it may be' it follows that it is not impossible, and from that it follows that it is not necessary;
Paragraph 8 Moreover the proposition 'it is not necessary that it should not be' is the contradictory of that which follows from the proposition 'it cannot be';
Paragraph 9 It may be questioned whether the proposition 'it may be' follows from the proposition 'it is necessary that it should be'.
Paragraph 10 Now both of these are false of that which necessarily is.
Paragraph 11 But in some cases the word is used equivocally.
Paragraph 12 Our conclusion, then, is this:
Paragraph 13 We may perhaps state that necessity and its absence are the initial principles of existence and non-existence, and that all else must be regarded as posterior to these.
Paragraph 14 It is plain from what has been said that that which is of necessity is actual.

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