ἘΠΕΙ δὲ περὶ ψυχῆς καθ’ αὑτὴν διώρισται καὶ περὶ
τῶν δυνάμεων ἑκάστης κατὰ μόριον αὐτῆς, ἐχόμενον ἐστι
ποιήσασθαι τὴν ἐπίσκεψιν περὶ τῶν ζῴων καὶ τῶν ζωὴν
ἐχόντων ἁπάντων, τίνες εἰσὶν ἴδιαι καὶ τίνες κοιναὶ πράξεις
αὐτῶν. Τὰ μὲν οὖν εἰρημένα περὶ ψυχῆς ὑποκείσθω, περὶ
δὲ τῶν λοιπῶν λέγωμεν, καὶ πρῶτον περὶ τῶν πρώτων. Φαίνεται δὲ τὰ μέγιστα, καὶ τὰ κοινὰ καὶ τὰ ἴδια τῶν
ζῴων, κοινὰ τῆς ψυχῆς ὄντα καὶ τοῦ σώματος, οἷον αἴσθησις
καὶ μνήμη καὶ θυμὸς καὶ ἐπιθυμία καὶ ὅλως ὄρεξις, καὶ
πρὸς τούτοις ἡδονή τε καὶ λύπη· καὶ γὰρ ταῦτα σχεδὸν
ὑπάρχει πᾶσι τοῖς ζῴοις.