In the Ethics the modern philosopher Baruch Spinoza produces an indubitable foundation for his metaphysics in the style of Euclidean proofs. One of the principal focuses of the Ethics is to show that God is Nature and Nature is God. Deus, sive Natura: “That eternal and infinite being we call God, or Nature, acts from the same necessity from which he exists” (Ethics, Part IV, Preface). Like Descartes and Leibniz, Spinoza was a rationalist, which meant he believed that all knowledge could be deduced from clear and distinct a priori self-evident truths.
The ancient Stoics would agree with Spinoza that God is Nature and Nature is God. The ancient Stoics used an a priori argument to prove the existence of God as a reasoning Universe. The Founder of the Stoic School, Zeno of Citium used the ontological argument to prove the Universe was a reasoning being. Zeno declared,
“That which exercises reason is more excellent than that which does not exercise reason; there is nothing more excellent than the universe, therefore the universe exercises reason” (Cicero, De Natura Deorum, ii. 8.; iii. 9).
Spinoza reasoned that everything is God because God is a substance with infinite mental and material attributes. Everything, even humans, owes its existence to God because all mental and material attributes constitute God. We are all tied together with the substance of Nature/God itself.
According to Spinoza, while we are absolutely determined both mentally and materially to be as we are, God, or Nature, is self-determined because God is a being from which all cause and effect relationships arise.
“From God’s supreme power, or infinite nature, an infinite number of things – that is, all things have necessarily flowed forth in an infinite number of ways, or always flow from the same necessity; in the same way as from the nature of a triangle it follows from eternity and for eternity, that its three interior angles are equal to two right angles” (Ethics, Part 1, XVII)
God is truly an infinite being that necessitates all truths both material and mental. All truths can be deduced from God the same way that in mathematics the sum of three interior angles of a triangle is deduced from the sum of two right angles.
It’s a shame we don’t have the complete works of the ancient Stoics but we know that they used a variety of methods to support their conclusion that the Universe is Divine and Providential. In addition to using the ontological-style argument, Zeno used an empirical argument from design,
“If melodiously piping flutes sprang from the olive, would you doubt that a knowledge of flute-playing resided in the olive? And what if plane trees bore harps which gave forth rhythmical sounds? Clearly you would think in the same way that the art of music was possessed by plane trees. Why, then, seeing that the universe gives birth to beings that are animate and wise, should it not be considered animate and wise itself” (Cicero, De Natura Deorum, II. 8)?
Unlike Spinoza, the Stoics used both a priori and a posteriori arguments to support their philosophical positions.
There’s no evidence the Stoics used the cosmological argument for the existence of God. It’s doubtful they would’ve used such an argument primarily because the Stoics did not believe that the Universe had a beginning since the eternal Divine Logos is an eternal fiery reasoning substance that flickers out (ending the universe) and then reignites again (recreating the universe) ad infinitum. Also, God and Nature are inseparable. The Universe is the necessary being that necessitates all things throughout Itself.
Despite different ways of justifying their pantheistic belief systems, Spinoza and the Stoics are on the same page that God is Nature and Nature is God. Marcus Aurelius put it poetically,
“Constantly regard the universe as one living being, having one substance and one soul; and observe how all things have reference to one perception, the perception of this one living being” (Meditations,