2.  Friends godly and well beloved, do, I implore you, beware of the shepherds of the Philistines; let them not choke your wills unawares; let them not befoul the purity of your knowledge of the faith.  This is ever their object, not to teach simple souls lessons drawn from Holy Scripture, but to mar the harmony of the truth by heathen philosophy.  Is not he an open Philistine who is introducing the terms “unbegotten” and “begotten” into our faith, and asserts that there was once a time when the Everlasting was not; cf. the Arian formula ἦν ποτὲ ὅτε οὐκ ἦν. that He who is by nature and eternally a Father became a Father; that the Holy Ghost is not eternal?  He bewitches our Patriarch’s sheep that they may not drink “of the well of water springing up into everlasting life,” John iv. 14. but may rather bring upon themselves the words of the prophet, “They have forsaken me, the fountain of living waters, and hewed them out cisterns, broken cisterns, that can hold no water;” Jer. ii. 13. when all the while they ought to confess that the Father is God, the Son God, and the Holy Ghost God, cf. p. 16, note.  This is one of the few instances of St. Basil’s use of the word θεός of the Holy Ghost. as they have been taught by the divine words, and by those who have understood them in their highest sense.  Against those who cast it in our teeth that we are Tritheists, let it be answered that we confess one God not in number but in nature.  For everything which is called one in number is not one absolutely, nor yet simple in nature; but God is universally confessed to be simple and not composite.  God therefore is not one in number.  What I mean is this.  We say that the world is one in number, but not one by nature nor yet simple; for we divide it into its constituent elements, fire, water, air, and earth. For the four elements of ancient philosophy modern chemistry now catalogues at least sixty-seven.  Of these, earth generally contains eight; air is a mixture of two; water is a compound of two; and fire is the visible evidence of a combination between elements which produces light and heat.  On the “elements” of the Greek philosophers vide Arist., Met. i. 3.  Thales (†c. 550 b.c.) said water; Anaximenes (†c. b.c. 480) air; and Heraclitus (†c. b.c. 500) fire.  To these Empedocles (who “ardentem frigidus Ætnam insiluit, c. b.c. 440) added a fourth, earth.  Again, man is called one in number.  We frequently speak of one man, but man who is composed of body and soul is not simple.  Similarly we say one angel in number, but not one by nature nor yet simple, for we conceive of the hypostasis of the angel as essence with sanctification.  If therefore everything which is one in number is not one in nature, and that which is one and simple in nature is not one in number; and if we call God one in nature how can number be charged against us, when we utterly exclude it from that blessed and spiritual nature?  Number relates to quantity; and quantity is conjoined with bodily nature, for number is of bodily nature.  We believe our Lord to be Creator of bodies.  Wherefore every number indicates those things which have received a material and circumscribed nature.  Monad and Unity on the other hand signify the nature which is simple and incomprehensible.  Whoever therefore confesses either the Son of God or the Holy Ghost to be number or creature introduces unawares a material and circumscribed nature.  And by circumscribed I mean not only locally limited, but a nature which is comprehended in foreknowledge by Him who is about to educe it from the non-existent into the existent and which can be comprehended by science.  Every holy thing then of which the nature is circumscribed and of which the holiness is acquired is not insusceptible of evil.  But the Son and the Holy Ghost are the source of sanctification by which every reasonable creature is hallowed in proportion to its virtue.