XXXIX. (203) After this the lawgiver proceeds to connect with these commandments a somewhat similar harmony or series of injunctions; commanding breeders not to breed from animals of different species; not to sow a vineyard so as to make it bear two crops at once; and not to wear garments woven of two different substances, which are a mixed and base work. Now the first of these injunctions we have already mentioned in our treatise on adulterers, in order to make it more evident, that our people ought not to be anxious for marriages with foreigners, corrupting the dispositions of the women, and destroying also the good hopes which might be conceived of the propagation of legitimate children. For the lawgiver, who has forbidden all copulation between irrational animals of different species, appears to have utterly driven away all adulterers to a great distance. (204) And we must now speak again of this rule in this our treatise on justice. For we must take care not to pass over the opportunity of adapting it to as many particulars as possible. It is just then to bring together those things which are capable of union; now animals of the same species are by nature capable of union, as, on the other hand, all animals of different species are incapable of any admixture or union, and the man who brings unlawful connections to pass between such animals is an injust man, transgressing the ordinances of nature; (205) but that which is the really sacred law takes such exceeding care to provide for the maintenance of justice, that it will not permit even the ploughing of the land to be carried on by animals of unequal strength, and forbids a husbandman to plough with an ass and a heifer yoked to the same plough, lest the weaker animals, being compelled to exert itself to keep up with the superior power of the stronger animal, should become exhausted, and sink under the effort; (206) and the bull is looked upon as the stronger animal, and is enrolled in the class of clean beasts and animals, while the ass is a weaker animal and of the class of unclean beasts; but nevertheless he has not grudged those animals which appear to be weaker, the assistance which they can derive from justice, in order, as I imagine, to teach the judges most forcibly, that they are never in their decisions to give the worse fate to the humbly born, in matters the investigation of which depends not on birth but on virtue and vice. (207) And resembling these injunctions is the last commandment concerning things yoked in pairs, namely, that it is unlawful to wear together substances of a different character, such as wool and linen; for in the case of these substances, not only does the difference prevent any union, but also the superior strength of the one substance is calculated rather to tear the other than to unite with it, when it is wanted to be used.