Yes, the entire superstructure of the edifice of Advita Vedanta is built on three words –‘Substance, Substratum and Show (or Appearance).’ These three words are very basic to its logic. All further development of its concepts, definitions and finer and more complex definitions of the doctrine depend on what the trio of words – Substance, Substratum and Show (or Appearance) – conveys.

Therefore, it is of utmost necessity that a student of Advaita should first have a clear and unambiguous grasp of what these words (or rather their equivalents in the original Sanskrit language) mean. Even a hair width of lack of clarity in understanding these three innocently looking words can lead to disproportionately disastrous misconceptions and misinterpretations of what Advaita is all about!

Let us first look at what any simple English dictionary gives the meaning of these three words to be. Starting there will help us appreciate better what the Sanskrit equivalents connote and how an aura of technicality surrounds those words when we use them in Advaita Vedanta.

Substance:

That which has mass and occupies space; the tangible matter of which a thing consists. Derived from Latin – substāre, to be present; to stand.          

Substratum (Same as Substrate):

Something that underlies or serves as a basis or foundation. Derived from Latin substrātus to lay under 

Show (or Appearance):

To cause or allow to be seen; display; appearance. Derived from  Old  English scēawian, to look at, display. To make, be, or become visible or noticeable. Derived from old High German scouwōn to look;

The three corresponding Sanskrit words for which they are used in Advaita Vedanta are:

vastu (substance); adhisThAna (substratum); and mAyA (show or display or appearance).

The meaning given to these three terms by Prof. John Grimes (JG) in his book on A Concise Dictionary of Indian Philosophy (1996) and by the Monier-Williams (MW) Sanskrit and English Dictionary (1899) are as follows:

vastu:

—  object or thing (JG);

—  any really existing or abiding substance or essence, thing, object, article; (in phil) the one real substance or essence which has no second (MW).

adhiSThAna:

—  basis; substratum; ground; according to Advaita Vedanta (JG);

—  a basis, base (MW).

mAyA:

—  the principle of appearance; illusion. According to Advaita Vedanta, it is the indeterminable principle which brings out the illusory manifestation of the universe; it is the device by which Advaitins explain how the one Reality appears as many (JG);

—  illusion, unreality, deception, fraud, trick, sorcery, witchcraft, magic; an unreal or illusory image, phantom, apparition (MW).

From the above listed meanings of the three words – Substance, Substratum (or Substrate) and Show (or Appearance), we can see that the common and popularly understood meanings in English change vastly and perhaps unrecognizably, when used in Advaita Vedanta. Therefore, English speakers, particularly, unfamiliar with the equivalent words in Sanskrit, may need to be extra cautious about their meaning when they are used in Advaita Vedanta. The two words, substance and substratum should not be interchanged or confused one for the other.

The next important point that has to be borne in mind is that the only True ‘Substance’ that IS is the Supreme Consciousness or Awareness or brahman. There is NO other really Real Substance, as per Advaita. brahman is the only really “Real Substance.”

What appears to us rock solid and physical, our day-to-day ‘world’ is, according to Advaita, a mere show or display or an appearance!

An ‘appearance,’ like a shadow play, is seen on a screen. So, we do not ask what is it made up of?

We will only ask what is the screen on which it appears. Advaita answers that question aptly. Consciousness or brahman is the screen! In other words, Consciousness is the substratum (in Sanskrit: adhiSThAna). We do not say It is the ‘vastu‘ for the appearance! Have you ever asked, when you walk in the Sun: “What is my shadow made up of?”

If the above aspect of the relationship between the appearance and substratum are firmly fixed in the mind of an Advaita student, the subsequent arguments of the Upanishads or Shankara commentaries become easy to appreciate.

Some of the Non-dual teachers and authors in the West often use the ‘modern’ computer screen metaphor to explain the appearance of the world. This metaphor tends to mislead the student in understanding the appearance of the world. In the appearance of an image or a document on the computer screen, the screen itself gets changed or modified to generate the appearing object at each pixel position. But According to Advaita Vedanta, Awareness or brahman is NOT a changeable entity. It is Absolutely immutable, indivisible. An appearance may get projected on to It, Itself being the ‘substratum.’ Therefore, the old cinema screen on to which an image from a film gets projected is a better metaphor to illustrate the world appearance on the substratum brahman.

In the light of such a clear understanding, the following lines of Shankara at 8.12.1, chAndogya Upanishad, stand out strikingly unique, highly meaningful, profoundly deep, and beautifully articulated. Shankara sums up the entire process from disembodiment to embodiment and back to disembodiment — the Supreme Consciousness to the individual to Supreme Consciousness, or brahman to the world of ignorance and back again to Self-knowledge:

“[T]his body is the abode – substratum (*to be understood as the supporting screen*) – of experiences of the Self. Or, it is the abode of the perceiving (Living) Self when He comes to be born, through fire, water, and the rest in that order. Or, the body may be regarded as the ‘abode’ of the Being, on the ground that the Being, in the form of the Living Self ‘abides’ in it.

“When the Self has for His abode such a body, which is constantly held by Death, and beset with pleasure and pain brought about by merit and demerit, then, abiding in such a body, He becomes ’embodied’. Though in His own nature, the Self is unbodied, yet He comes to have such notions as “I am the body and the body is myself,” on account of His not understanding His real nature.

This is what is meant by His becoming bodied. Hence, having thus become bodied, He becomes held by pleasure and pain. This is a well-known fact for this bodied Being, there is no getting rid of destruction, removal of pleasure and pain, caused respectively by the connection and disconnection of external things and appearing in a continuous series, which connection and disconnection He regards as His own. The same Being, however, when, His ignorance in the shape of His notion of the body being the Self has been set aside by His Knowledge of His real unbodied nature, then pleasure and pain do not touch Him.” (Translation: Dr. G.N. Jha).

And that’s what is Self-realization.

[The words within the stars in the parenthesis are added by me for clarity.]