[B]Note: This is re-posted here with slight modifications for ease of future reference[/B]
One of the most important features of the theory of existent effects is that it is based observations of nature. No effect that exists in nature can be produced from sheer non-existence, everything has a material cause. A table is produced from wood, wood comes from trees, trees come from seeds. But you cannot produce an apple tree from an oak seed, you can’t produce iron from lead, you can’t produce a pig from a rock. An effect can only be produced from a material that is competent to produce it.
The natural progression of cause and effect leads to the question of what is the ultimate material cause, beyond which no further reduction of matter can be made. In Samkhya, the name given to this first cause is Prakriti. Samkhya also observed that the spirit or self of living beings is not material in nature, but something fundamentally different called Purusa. They reasoned that Prakriti cannot be an effect of Purusa, because Purusa is not a material that is competent to produce it. This leads to the natural and intuitive conclusion that spirit and matter, though fundamentally different, are equally real.
What does Vedanta have to say about this? The following is a quote from the Brahma Sutra, an authoritative document of Vedanta:
We can see clearly that the primary objection to the Samkhya theory of Prakriti (Pradhana) is that it is contrary to the Upanishads. This is a huge difference in approach. Samkhya starts with observation and uses reason to draw inferences about the nature of reality. Vedanta starts from scripture and uses reason to rationalize it. The unhappy consequence of this is that it leads to conclusions that are counterintuitive, unnatural, contrary to experience, and wrong.
Here we can see that Surya Deva has missed the main point of the Theory of Existent Effects, which is that an effect can only be produced from a material that is competent to produce it. His rationale is motivated by the need to defend the authority of the Upanishads, which say that Brahman is the cause of the universe. He doesn’t really provide any valid reasoning, he just says, this is not possible, it makes no sense. Samkhya explains how it is possible.
The theory of Prakriti states that it has three constituent substances called gunas, and that all of the manifestations of nature occur through different combinations of the gunas in which one or the other predominates. In the root Prakriti, which is unmanifest, the gunas are said to be in equilibrium, and when the balance is disturbed Prakriti begins to manifest. So even though it is unmanifest, the root Prakriti is still a material that is competent to produce the effects of manifest nature.
This directly answers the question how does an unmanifest something produce a manifest something? The short answer is, when Prakriti is unmanifest, the gunas are in equilibrium. When the equilibrium is disturbed, the gunas begin to manifest. But it begs the question, what causes the equilibrium to be disturbed? This is answered by thetheory of the emergent Isvara.
Now that we understand the gunas, we can refine the definition of Purusa to [I]that which is [B]not[/B] composed of the gunas[/I]. This makes it more clear that Purusa is not a material that is competent to produce the effects of nature.