Book,  Paragraph

 1   I,  4 |   everything either because it is necessary or because it is better
 2   I,  4 |       reasons. But that it is not necessary for generation is plain;
 3   I,  6 |        and secondly because it is necessary that their copulation should
 4   I,  15|      their arms. This attitude is necessary, because Nature has bent
 5   I,  15|          at this point, for it is necessary, if the male discharges
 6   I,  19|        laid down. But since it is necessary (1) that the weaker animal
 7   I,  21|         plain then that it is not necessary that anything at all should
 8   I,  23|       live; therefore, when it is necessary for it to accomplish the
 9  II,  1 |   naturally perfect). And this is necessary for the reason that whenever
10  II,  3 |    residing in it? It is not only necessary to decide whether what is
11  II,  3 |           in actuality. And it is necessary either (1) that they should
12  II,  3 |          others not. Again, it is necessary that they should either (
13  II,  4 |           of all cases when it is necessary to move anything, because
14  II,  4 |          female. Thus while it is necessary for the female to provide
15  II,  4 |          material mass, it is not necessary for the male, because it
16  II,  4 |          round it; this is both a necessary result and for a final cause,
17  II,  4 |   separating from the rest, it is necessary that this principle should
18  II,  6 |         well nor do they assign a necessary cause who say simply that "
19  II,  6 |          to the parts which it is necessary to move, for it is late
20  II,  6 |          superfluous. Hence it is necessary that the eyelids should
21  II,  6 |   concocted, those which are only necessary for the sake of the former
22  II,  8 |         it entirely so it is only necessary that its generative secretion
23 III,  2 |       point than below, for it is necessary to shelter and protect this
24 III,  10|         copulation, then as it is necessary that the same account should
25 III,  10|        due order, therefore it is necessary that it should be denied
26  IV,  1 |      these parts, as if it were a necessary consequence for this part
27  IV,  1 |          one another. If so it is necessary that the sexual parts like
28  IV,  1 |         than one)—therefore it is necessary that both female and male
29  IV,  1 |    opposite of what it was, it is necessary also that what is not under
30  IV,  3 |           other such cause, it is necessary that animals should produce
31  IV,  3 |           monstrosity, though not necessary in regard of a final cause
32  IV,  3 |          cause and an end, yet is necessary accidentally. As for the
33  IV,  4 |       such cases it is absolutely necessary that this should occur when
34  IV,  4 |         considered as eternal and necessary, but we speak of things
35  IV,  4 |          emits more semen than is necessary, or more powers in different
36  IV,  5 |          are both greater than is necessary for one embryo, only not
37  IV,  8 |     happen also as being due to a necessary cause. For at first such
38  IV,  8 | discharged from the mother, it is necessary that the residual matter
39   V,  1 |          the other hand, if it is necessary that the animal should have
40   V,  1 |           cannot be broken.~It is necessary then for the embryo animal
41   V,  1 |         be transparent, and it is necessary that the transparent should
42   V,  3 |        circumstances and for what necessary causes each particular kind
43   V,  8 |           in each case. And it is necessary, if an animal is to obtain
44   V,  8 |           of Nature. Now they are necessary, it is true, but yet they