Plutarch, De Iside et Osiride 56 (part 1)

ἡ δὲ κρείττων καὶ θειοτέρα φύσις ἐκ τριῶν ἐστι, τοῦ νοητοῦ καὶ τῆς ὕλης καὶ τοῦ ἐκ τούτων, ὃν κόσμον Ἕλληνες ὀνομάζουσιν. ὁ μὲν οὖν Πλάτων τὸ μὲν νοητὸν καὶ ἰδέαν καὶ παράδειγμα καὶ πατέρα, τὴν δʼ ὕλην καὶ μητέρα καὶ τιθήνην ἕδραν τε καὶ χώραν γενέσεως, τὸ δʼ ἐξ ἀμφοῖν ἔκγονον καὶ γένεσιν ὀνομάζειν εἴωθεν. Αἰγυπτίους δʼ ἄν τις εἰκάσειε τῶν τριγώνων τὸ κάλλιστον μάλιστα τούτῳ τὴν τοῦ παντὸς φύσιν ὁμοιοῦντας, ὡς καὶ Πλάτων ἐν τῇ πολιτείᾳ δοκεῖ τούτῳ προσκεχρῆσθαι τὸ γαμήλιον διάγραμμα συντάττων. ἔχει δʼ ἐκεῖνο τὸ τρίγωνον τριῶν τὴν πρὸς ὀρθίαν καὶ τεττάρων τὴν βάσιν καὶ πέντε τὴν ὑποτείνουσαν ἴσον ταῖς περιεχούσαις δυναμένην. εἰκαστέον οὖν τὴν μὲν πρὸς ὀρθὰς ἄρρενι, τὴν δὲ βάσιν θηλείᾳ, τὴν δʼ ὑποτείνουσαν ἀμφοῖν ἐκγόνῳ· καὶ τὸν μὲν Ὄσιριν ὡς ἀρχήν, τὴν δʼ Ἶσιν ὡς ὑποδοχήν, τὸν δʼ Ὧρον ὡς ἀποτέλεσμα. τὰ μὲν γὰρ τρία πρῶτος περισσὸς ἐστι καὶ τέλειος· τὰ δὲ τέτταρα τετράγωνος ἀπὸ πλευρᾶς ἀρτίου τῆς δυάδος· τὰ δὲ πέντε πῆ μὲν τῷ πατρὶ πῆ δὲ τῇ μητρὶ προσέοικεν, ἐκ τριάδος συγκείμενα καὶ δυάδος. καὶ τὰ πάντα τῶν πέντε γέγονε παρώνυμα, καὶ τὸ ἀριθμήσασθαι πεμπάσασθαι λέγουσιν. ποιεῖ δὲ τετράγωνον ἡ πεντὰς ἀφʼ ἑαυτῆς, ὅσον τῶν γραμμάτων παρʼ Αἰγυπτίοις τὸ πλῆθός ἐστι, καὶ ὅσων ἐνιαυτῶν ἔζη χρόνον ὁ Ἆπις. τὸν μὲν οὖν Ὧρον εἰώθασι καὶ Μὶν προσαγορεύειν, ὅπερ ἐστὶν ὁρώμενον· αἰσθητὸν γὰρ καὶ ὁρατὸν ὁ κόσμος. ἡ δʼ Ἶσις ἔστιν ὅτε καὶ Μοὺθ καὶ πάλιν Ἄθυρι καὶ Μεθύερ προσαγορεύεται·

The better and more divine nature consists of three parts: the conceptual, the material, and that which is formed from these, which the Greeks call the world. Plato is wont to give to the conceptual the name of idea, example, or father, and to the material the name of mother or nurse, or seat and place of generation, and to that which results from both the name of offspring or generation. One might conjecture that the Egyptians hold in high honour the most beautiful of the triangles, since they liken the nature of the Universe most closely to it, as Plato in the Republic seems to have made use of it in formulating his figure of marriage. This triangle has its upright of three units, its base of four, and its hypotenuse of five, whose power is equal to that of the other two sides. The upright, therefore, may be likened to the male, the base to the female, and the hypotenuse to the child of both, and so Osiris may be regarded as the origin, Isis as the recipient, and Horus as perfected result. Three is the first perfect odd number: four is a square whose side is the even number two; but five is in some ways like to its father, and in some wrays like to its mother, being made up of three and two. And panta (all) is a derivative of pente (five), and they speak of counting as numbering by fives. Five makes a square of itself, as many as the letters of the Egyptian alphabet, and as many as the years of the life of the Apis. Horus they are wont to call also Min, which means seen; for the world is something perceptible and visible, and Isis is sometimes called Muth, and again …