Real friendship, however, supposes the power of reflection; it is of all attachments the most worthy of man, and the only one by which he is not degraded. Friendship flows from reason alone. It is the mind of a friend which we love, and to love a mind it is necessary to have one, and to have made use of it in the attainment of intelligence, and in comparing the congeniality of different minds. By friendship, then, not only is implied the principle of knowledge, but also, from reflection, the actual exercise of that principle. Thus, while friendship belongs solely to man, attachment may be possessed by animals; as sentiment alone is sufficient to attach them to persons whom they often see, and by whom they are fed and nourished. The attachment of females to their young is produced by the trouble they have had in carrying them in the womb, and in producing and giving them suck. If, among birds, some males seem to have an attachment to their young, and to take care of the females while they are sitting, it is because they have been employed in the construction of the nest, and continue to enjoy pleasure with their females long after impregnation. Among other animals, with whom the season of love is short, that elapsed, the male is no longer attached to the female; where there is no nest, no employment, in which they may be mutually engaged, the fathers, like those of Sparta, have no care for their progeny. The pride and ambition of animals proceed from their natural courage; that is, from their sense of their strength, agility, &c. Large ones hold the small in defiance, and seem to contemn their insulting audacity. This courage may also be improved by instruction, for, reason alone excepted, of every thing are brute animals susceptible. In general they will learn to perform the same action a thousand times; to do without intermission what they did by intervals; to continue for a length of time what they at first ended in a moment; to do cheerfully what at first was the effect of force; to do by habit what they once have done by chance; and to perform of themselves what they have seen done by others. Of all the operations of the animal machine imitation is the most admirable. It is its most delicate and most extensive mobile, and exhibits the truest copy of thought, and though the cause of it in animals is altogether material, yet by its effects our wonder is excited. Men never more admire an ape than when they see it imitate the actions of men. In fact it is not easy to distinguish some copies from some originals. Besides, there are so few who can distinctly perceive the difference between a reality and a counterfeit, that to the bulk of mankind an ape must always excite astonishment.