Illusion is false knowledge based on an untrue form
Illusion (viparyaya) is false knowledge (mithyā-jñāna) based on an untrue form.
Having explained right knowledge, now is described the mental process called illusion: it is false knowledge based on an untrue form.
(Opponent) Our subject is inhibition, and furthermore the release which comes from it, and furthermore the bondage to be escaped from, and furthermore the Ignorance (avidyā) which is the root of bondage. Ignorance is illusion, so this is the main thing to be inhibited. For it is the cause of bondage, and when the cause is inhibited, it follows that its effect is inhibited also. So illusion is the principal thing and should have been explained before right knowledge.
(Answer) Certainly illusion is the first thing as regards needing inhibition. But human efforts at inhibition are based on knowledge of what is correct and what is faulty, and that knowledge of the correct and faulty must be right knowledge. Without right knowledge, the evils of illusion would not be realized, nor would one know about inhibition and the means leading to it. So it was proper to take the mental process of right knowledge first. What is correct and what is erroneous are known by right knowledge; illusion is described immediately afterwards, as more important than any of the remaining mental processes. The reason is that inhibition of illusion must precede that of the others, since it is their root.
Illusion is false knowledge, they are synonyms, based on an untrue form, is the definition. The form of a thing is the true form, and what is not its form is an untrue form of it, an experience of a semblance of it (yad-ābhāsam vijñānam); the basis of the experience is that on which it rests.
Illusion is an idea which has merely a common element with something of which the particular is not now being perceived, which is aided with the memory of another thing experienced previously, associated with the definite form of it, and arising with an appearance of certainty.
Doubt has the form ‘there is this similarity between the two things’, and it arises in the mind of one who seeks to know, when seeing the similarity, which of the two things it is; doubt is classed purely as memory. The doubt ‘Is this a post or a man?’ arises only from the memory of the previously perceived individual things. Not so illusion, for there just one of the memories becomes conclusive. In a place where a post has been set up at some time, there arises the definite idea ‘this is a man’, coming from the memory of a man aroused by perception of something of the appropriate height and breadth and so on.
Although illusion is in the main like something perceived by way of the senses, it is not right knowledge because it is based on a memory of something not now there.
Why is it not right knowledge? Because it is negated by right knowledge. The object of right knowledge is a thing as it is, and the fact of not being right knowledge is shown by the fact that right knowledge cancels it. For instance, seeing the moon as double is negated by seeing that it is in fact a single moon.
Because it is negated by right knowledge: it is no more than a memory and its object is not an actual thing. For an object which is merely remembered is not there now.
(Opponent) So it turns out to be no more than a memory.
(Answer) No, because it distinctly appears. A memory is caused by a thing having been perceived in another place, and appears in the form ‘this is how it was experienced’. An illusion is not like that. The illusion-idea arises when there is what amounts to a memory, possessing a close similarity and conformity in time and place etc. to some thing (now being perceived), and appearing distinctly as ‘this’. Thus illusion has neither the character of right knowledge, nor that of memory, and is a separate kind of mental process.
Now the commentator gives an example to show how what is not right knowledge is negated by right knowledge. Just as seeing the moon as double is negated by seeing that it is in fact a single moon. If diseased vision sees things otherwise than as they are, sees (for instance) the moon as double, then by apprehending what it really is, the thing as it is, a single moon, the false view is negated. It is negated by means of the memory of the knowledge that the apparent second moon is really non-existent.
(Opponent) On a grammatical point: dvi-candra-darśanam (seeing a double moon) is a dvigu compound of the same class as dvipūlī (two bundles) or pañcapūlī (five bundles), as we learn from the Pāṇini sūtra 2.4.1, which teaches that where the last element ends in the letter ‘a’, the compound preferably takes the feminine form (i.e. the final ‘a’ becomes ‘ī’). The word dvi-candra is a dvigu compound ending in ‘a’, and ought to have had the ‘ī’ ending.
(Answer) The form is not wrong because Pāṇini allows exceptions, for pātra etc., and the word etcetera there refers to a whole class. This class retains the final ‘a’ and is in accordance with the usage of the learned, and the compound dvi-candra should be taken as included in it. It is the type of compound called bahuvrīhi, and means the seeing in which there are two moons. It is unquestionable that the compound eka-candra (one-moon) is never a dvigu.
And this is the Five-fold Ignorance (avidyā), namely the taints (kleśa): Ignorance, I-am-ness, passion, hate, clinging to life. These have technical names: darkening, delusion, great-delusion, darkness, blind darkness. They will be discussed later, under defilements of the mind.
This illusion is Ignorance, of which there are five parts. As to what they are, they will be listed (in sūtra II.3): Ignorance, I-am-ness (asmitā), passion (rāga), hate (dveṣa), and clinging to life (abhiniveṣa). Ignorance and the others are taints which are each distinguished by a special technical name, defined in other classics as darkening (tamas) and the others, and they will be described in the second part as associated with the impurities of the mind.