Though the word khyāti literally means knowledge, it is often used as a technical term indicating a theory that purports to explain erroneous perception or illusion. Such a perception, though a fact of experience, defies all attempts at explaining it. When the snake is seen in a rope in insufficient light, or silver in nacre in moonlight, it is difficult to say how exactly it happens.
The various schools of Indian philo-sophy have dealt with this problem and have given different explanations of it. These explanations naturally vary according to their epistemological and metaphysical views. Each school has also tried to defend its position and refute the theories of others.
The main points of controversy are concerned with the nature of the illusory object and how it is caused.
The seven such khyātis or theories will now be dealt with in the alphabetical order:
- Akhyāti (‘non-apprehension’): This is the theory propounded by the Mīmāṁsā school of Prabhākara. ‘Viveka-akhyāti-vāda’ is another name for the same. According to this view, it is the akhyāti or non-apprehension of the difference between the memory-image of silver and nacre the percept, that is responsible for the illusion of silver in the nacre.
- Anirvacanīyakhyāti (‘apprehension of the indefinable’): According to this theory advocated by the Advaita Vedānta, the illusory object like silver is an instantaneous and apparent creation of ajñāna or ignorance associated with the substratum like nacre. Since the silver is perceived, it is not asat or unreal like the son of the barren woman. Since it is sublated by the later, correct, perception of nacre, it is not sat or real either. Nor can it be both sat and asat simultaneously which is contradictory. Hence it should be described as anirvacanīya, indefinable. The theory itself which holds the illusory object as anirvacanīya, is known as anirvacanīya-khyāti.
- Anyathākhyāti (‘misapprehension’): This theory also called ‘viparītakhyāti,’ is put forward by the Nyāya school, the school of Indian logic. Nacre is apprehended as anyathā, as something else. This misapprehension is caused by defective eyesight or insufficient light. The reflection of the nacre in moonlight due to its similarity to silver, brings on the memories of silver perceived earlier. The silver of memory, of a past experience, is superimposed on the nacre, or the present experience. Though both objects are real, the mistake consists in superimposing one upon the other, forgetting the time and place factors.
- Asat-khyāti (‘apprehension of the non-existent’): The nihilistic school of Buddhism, called the Mādhyamika school, propounds the theory that nothing really exists. In illusory perception, an asat or a non-existent like silver is apprehended as existent. Hence the name ‘asat-khyāti’, apprehending what does not really exist. Really speaking, even the nacre is unreal or non-existent. Hence both—the object of illusion and its substratum—are non-existent!
- Ātma-khyāti (‘apprehension of the subjective cognition’): As against the nihilism of the Mādhyamika school, subjective idealism of the Yogācāra school of Buddhism affirms the existence of internal ideas but denies external objects. Externalization of the internal cognitions is the real mistake in all perceptions whether ‘normal’ or ‘illusory’. The silver as well as nacre is an internal idea only. This theory of illusion is known as ātma-khyāti.
- Sadasat-khyāti (‘apprehension of the real-unreal’): This theory is propounded by the Sāṅkhya school of Kapila. In the illusory perception ‘This is silver’, the cognition of ‘this’ is real since the object nacre is present to the organ of vision. But, the cognition of ‘silver’ is unreal since it is not present to the organ of vision. Hence it is a case of apprehending the sad-asat, or real-unreal.
- Sat-khyāti (‘apprehension of the real’): What is perceived as real, must have its basis in a real object. If silver is perceived in the nacre, it must be present there, however small may be the quantity. This is possible since the funda-mental components of both nacre and silver (viz., the five elements of earth, water and so on) are the same. The perception is false only in the sense that the silver does not serve any practical purpose. This is the view of the Viśiṣṭādvaita school of Vedānta propagated by Rāmānuja, called sat-kyāti.