But since our argument discovered in our vital faculty three different varieties-one which receives nourishment without perception, another which at once receives nourishment and is capable of perception, but is without the reasoning activity, and a third rational, perfect, and co-extensive with the whole faculty-so that among these varieties the advantage belongs to the intellectual,-let no one suppose on this account that in the compound nature of man there are three souls welded together, contemplated each in its own limits, so that one should think man's nature to be a sort of conglomeration of several souls. The true and perfect soul is naturally one, the intellectual and immaterial, which mingles with our material nature by the agency of the senses; but all that is of material nature, being subject to mutation and alteration, will, if it should partake of the animating power, move by way of growth: if, on the contrary, it should fall away from the vital energy, it will reduce its motion to destruction. Thus, neither is there perception without material substance, nor does the act of perception take place without the intellectual faculty.

Ἐπειδὴ δὲ τρεῖς κατὰ τὴν ζωτικὴν δύναμιν διαφορὰς ὁ λόγος εὗρε͵ τὴν μὲν τρεφομένην χωρὶς αἰσθήσεως͵ τὴν δὲ τρεφομένην μὲν καὶ αὐξανομένην͵ ἀμοιροῦσαν δὲ τῆς λογικῆς ἐνεργείας͵ τὴν δὲ λογικὴν καὶ τελείαν δι' ἁπάσης διήκουσαν τῆς δυνάμεως͵ ὡς καὶ ἐν ἐκείναις εἶναι καὶ τῆς νοερᾶς τὸ πλέον ἔχειν, μηδεὶς διὰ τούτων ὑπονοείτω τρεῖς συγκεκροτῆσθαι ψυχὰς ἐν τῷ ἀνθρωπίνῳ συγκρίματι͵ ἐν ἰδίαις περιγραφαῖς θεωρουμένας͵ ὥστε συγκρότημά τι πολλῶν ψυχῶν τὴν ἀνθρωπίνην φύσιν εἶναι νομίζειν. Ἀλλ' ἡ μὲν ἀληθής τε καὶ τελεία ψυχὴ μία τῇ φύσει ἐστίν͵ ἡ νοερά τε καὶ ἄϋλος͵ ἡ διὰ τῶν αἰσθήσεων τῇ ὑλικῇ καταμιγνυμένη φύσει. Τὸ δὲ ὑλῶδες ἅπαν ἐν τροπῇ τε καὶ ἀλλοιώσει κείμενον͵ εἰ μὲν μετέχοι τῆς ψυχούσης δυνάμεως, κατὰ αὔξησιν κινηθήσεται, εἰ δὲ ἀποπέσοι τῆς ζωτικῆς ἐνεργείας͵ εἰς φθορὰν ἀναλύσει τὴν κίνησιν. Οὔτε οὖν αἴσθησις χωρὶς ὑλικῆς οὐσίας͵ οὔτε τῆς νοερᾶς δυνάμεως χωρίς͵ αἰσθήσεως ἐνέργεια γίνεται.