At what time especially should human generation take place?
discussion, then, concerning the principle of human [generation]," etc. In this ninth book one asks first, at what time human generation especially should take place.
1. And it seems that it should take place during adolescence, because generation ought to occur more or especially during a time when the material for generation is more abundant. But this material is moisture, and moisture is more abundant during adolescence. Therefore, etc.
2. In addition, heat is the effective principle of generation. But heat is more abundant during adolescence, which is clear from a human's growth pattern. And this is why, etc.
3. Moreover, pleasure is more abundant at this time, and the greatest pleasure occurs during a time of generation. Therefore, etc.
The Philosopher says the opposite. For he says that the period most suitable for generation occurs at the end of the third seven-year period.
One must reply that generation is of two types. One is of a complete fetus, and the other is of an incomplete fetus. The first type in particular has to occur at the end of the third seven-year period, because when the nutritive power and the power of growth are bounded, then the generative power begins. But at this time growth is bounded, and this is why generation begins, because the seed, which is the principle of generation, is a superfluity of the aliment. But during the period of growth there is little of this superfluity because the whole of the aliment is converted into the substance of the members. Generation in the second sense, however, begins at the end of the second seven-year period, because it is then that the seed begins to move and likewise the menses. Yet in truth these are not well ordered or made firm then, and this is why in this period the fetus is weak and poorly disposed.
1. To the first argument one must reply that too much moisture dulls the heat and a great deal of heat is necessary for generation. Therefore, although moisture abounds during adolescence, nevertheless it dulls the heat, and generation is therefore weakened. And in the same way one can say that moisture is of two types. One type is the material for the nutriment, and this is abundant in adolescents. The other is the material for generation, and this one is abundant after the third seven-year period.
2. To the second argument one must reply that heat can be said to be greater in two ways: either qualitatively or quantitatively. It is quantitatively greater in adolescents, but it is qualitatively less because it is curbed by moisture, which is its contrary.
3. To the third argument one must reply that pleasure is of two types: ordered, which occurs in men, and disordered, which occurs in adolescents.
Whether a difference in ages ought to be calculated according to seven-year periods.
Further one inquires whether a difference in ages ought to be calculated according to seven-year periods.
And it seems not, for the moon has dominion over everything moist, because it is the mother of the waters. And the moon varies according to its four phases. Therefore, ages and other dispositions containing moisture have to be calculated according to a number containing four.
In addition, illness is indicated through the number seven or by a seven-day period, and therefore for the same reason so too is age.
The opposite is apparent according to the Philosopher. One must reply that a given disposition, such as illness, has its cause in matter just as in a subject and this is why it lasts for a shorter period and then ends. But there is another disposition that is caused by the consumption of moisture and natural heat, and a disposition like this requires a longer period of time for its onset, because the first one can be introduced from an indisposition of the moisture or of accidental heat. Illness is introduced in the first way, and age in the second way, and this is why illness is introduced according to days, and age according to years. But the moon has dominion over everything moist through its four phases, but its four phases are measured or counted in periods of seven days.
And in this way a solution is apparent for the arguments.