His first great assertion is that "It is". "It", i.e. Reality, Being, of whatever nature it may be, is, exists, and cannot not be. It is, and it is impossible for it not to be. Being can be spoken of, and it can be the object of my thought. But that which I can think of and can speak of can be, "for it is the same thing that can be thought and can be". But if "It" can be then it is. Why? Because if it could be and yet were not, then it would be nothing. Now, nothing cannot be the object of speech or thought, for to speak about nothing is not to speak, and to think faout nothing is the same as not thinking at all. Besides if it merely could be, then, paradoxically, it couldnever come to be, for it would then have to come out of nothing, and out of nothing comes nothing and not something. Being, then, Reality, "It" was not first possible, i.e. nothing, and then existent: it was always existent - more accurately, "It is".
In the Sankhya-karikas of Isvarakrishna we have this expression of the doctrine of Satkaryavada also known as the doctrine of the non-difference of cause and effect:
The effect already exists in the cause for the following reasons: what is nonexistent cannot he produced; for producing a thing, a specific material cause is resorted to; everything is not produced by everything; a specific material cause capable of producing a specific product alone produces that effect; there is such a thing as a particular cause for a particular effect.
As in the injunction frequently encountered on Irish building sites Think of the next man, this doctrine leaves much to be done in the way of ingenious exegesis by subsequent sages. We can however discern through the fog something of the form of a like insight to that of Parmenides. What is, is, and what is not has no traction on reality in order to come to be. It can't get started.
As mentioned in a previous note on this topic
advaitic causalitythis idea of causality comes from the narrow focus of what in the Aristotelian system would be termed material causality. In a curious way the materialist monism of Parmenides throws a light on the Satkaryavada doctrine which bundles together material and efficient causality and treats them as one. Because potential is wrapped up in the nature of the material which is then what is to be formed out of that material must somehow be in existence. Otherwise it could not come to be because it would be nothing and as we are told nothing cannot gain traction.
Satkaryavada is a confused likeness of the doctrine of the impossibility of change espoused by Parmenides in that it accepts change but only as mithya i.e. real as an appearance.
By knowing a single lump of clay, everything that is made of clay would become known. A modification begins with speech, it is a (mere) name. The clay alone is true i.e. real.Commentary on Chandogya Upanishad VI.i.4
In the commentary of Shankara on the Brahma-Sutra-Bhasya the impossibility of something coming out of nothing is unequivocally stated.
Existence does not come out of non-existence. If something can come out of nothing, then it becomes useless to refer to special kinds of causes, since non-existence as such is indistinguishable everywhere.B.S.B. II.ii.26
This general principle is used externsively both in the discussion about material causality and the possibility of change and also as a method of refutation of the Buddhist doctrines of Annata and Annica. In this note I am concerned with material causality. An important citation on this topic is B.S.B. II.i.18 in which he states his views on potency:
Again, when some potency is assumed in the cause, to determine the effect, that potency cannot influence the effect by being different (from the cause and effect) or non-existent (like the effect), since (on either supposition) non-existence and difference will pertain to the potency as much as to the effect. Therefore the potency must be the very essence of the cause, and the effect must be involved in the very core of the potency.
Grasping these ideas is like lifting mercury with a fork because we are so primed with the Aristotelian concept of Cause & Effect. I'm not even sure that they conflict with Aristotle's views because they are more onto-theological than ontological. Brahman in the Vedic schema is the material cause of the universe. Brahman as pure act is the cause and the effect of all manifestation. Just as all the potential for items made of clay is in the clay, all the potential for what is, is in Brahman. There is a unity of act and potency in Brahman and because Brahman is the reality of anything whatever this non-difference of cause and effect is reflected in matter of all kinds.
It is not the case that Shankara ignores the idea of efficent causality claiming that everything just happens. He accepts the role of actors but still subordinates their causal importance to the material cause or the nature of things. That is the supervenient reality.
Moreover, if it be admitted that something can come out of nothing, then on the same ground even the indifferent people who are inactive should attain their desired results, for non-existence is clearly evident even there, and so a husbandman who does not engage in cultivation should get his crop, a potter who makes no effort for preparing the clay should get his vessels ready, and a weaver who does not make any effort for weaving the yarn should get a cloth just as much as one that weaves. And nobody need in any way strive for heaven or liberation. But such a position is neither reasonable nor is accepted by anybody. Therefore the assertion of something coming out of nothing is unjustifiable.
These topics of substance, identity and change refracted through a vedic medium are puzzling and pondering on them gives one a sense of how Plato confronted by Parmenides tried to save the appearances.