Pratyaksha or Perception implies direct, immediate cognition. There are two kinds of direct perception, external and internal. The ‘external’ perception implies cognition of sense objects, namely – sound, touch, form, taste and smell by our five sense organs or gyanendriyās – ears, skin, eyes, tongue and nose. When the sense organs contact their respective objects then the Pratyaksha knowledge takes place. The ‘internal’ perception means the direct & immediate cognition of pain, pleasure, love, hate, anger, knowledge or ignorance of various objects etc. in & by our minds. Pratyaksha Pramāņa is possible only when the sense organ, the mind and the context of the interaction are all in perfect condition. A knowledge established by pratyaksha pramāņa under these conditions is called Samyajnyāna (samyak+jnyāna); Otherwise, even pratyaksha may lead to mithya jnyāna (mis-understanding) or samshaya jnyāna (uncertain knowledge).
It is in our experience to know an object or issue other than interaction with the sense objects. For example, if we see smoke, we may infer that there must be fire. This is because, it has been our experience that, smoke is associated with fire. Thus, the ability to know an object by its relationship with another object is anumāna pramāņa. However, anumāna has to be confirmed by pratyaksha pramāņa, because if we were to follow the smoke and find no fire, the anumāna pramāņa, that it is fire, is negated. Pratyaksha anumāna is therefore called the Nirankusha (independent) pramāņa, for it cannot be negated by any other pramana whereas anumāna pramana can be negated by pratyaksha pramana.
Sabda is verbal testimony. It is also called ‘apta-vakyas’ (statement of a trust-worthy person’, and agama (authentic word) or Shruti. A verbal statement, uttered or written, is man’s most potent instrument for transmitting knowledge. We learn mostly by means of words. An oral or written message is a universal mode of communication. We constantly get various information, direction & knowledge through words. Right from school days to this moment we use words as a valid & effective means of bringing about awareness of things, ideas or emotions. Books, magazines, newspaper, letters, conversations, chats, radio, TV, movies, songs etc. etc. All use or depend on words. We cannot do without verbal testimony. When it comes to issues beyond the reach of human mind or intellect, sabda pramāņa is the only means to acquire the knowledge of that issue or object.
Shruti has been accepted as the final source, since it is apourusheya – not created by any human/humans. They are the statements of Brahman, presented along with creation. The following five rationales have been offered to establish the apourusheya nature of Agama. Firstly, there is no authorship for vedas – If there was an author, the human ego would have revealed it. Secondly, they are so comprehensive that no single human could have composed them. Thirdly, there are no contradictions in the shrutis which rules out possibility of multiple human authors; if there were multiple authors, contradictions would be the norm. Fourthly, its spelling, punctuations and intonations have been retained over time. Finally, a human composition could not have survived in original form over time. Therefore issues related to dharma, nature of Brahman and jiva have to be understood through Agama pramāņa.
Knowledge obtained by comparing an unknown object with a known object is called upamāna pramāņa. upa is near or close (known in this context) and mana is to understand; thus upamāna is knowledge by comparing to a known object. upamāna has limitations and cannot be all encompassing. For instance, A man, who does not know what a wild cow is, may be told by someone that it is an animal like the cow. If subsequently he happens to meet with such an animal in the forest and knows or recognizes it as a wild cow, then his knowledge will be due to upamāna or comparison. Another example, Suppose you do not know what ‘saxophone’ means. You may be told by a musician: ‘A saxophone is a musical instrument something like an Ushaped trumpet.’ If, on subsequently seeing a saxophone, you are able to give its name, it will be clear that you understand what ‘saxophone’ means. Now, upamāna is just this way of knowing the denotation of words, or the relation between names and the objects denoted by them. The Nyāya school for instance reduces Upamana to Anumāna, thus indicating that they are not mutually exclusive.
This means postulation, supposition or presumption of a fact. It is a distinct valid method of mediate knowledge. It is in fact a method of assumption of an unknown fact in order to account for a known fact that is otherwise inexplicable. The classic example of this method of knowledge is a fat person A says that he never eats in the day, then we can easily postulate that he eats in the night, for the simple reason that without this assumption his fatness & also his getting fatter cannot be explained. Arthapatti can either be from what is seen or from what is heard. The use of this method in Vedanta is in assuming rightly the implications of Upanishadic statements. Like in the statement ‘The knower of Self transcends grief’. Here we see that merely knowledge destroys grief, then it can be assumed without any doubt, that all grief has to be false then alone it can be destroyed merely by knowledge. The legal system uses this extensively, when the statements of a witness are inconsistent with the findings, say by investigators. Some schools argue that Arthapatti is no different from Anumāna.
Anupalabdhi means non-apprehension or absence. The Advaitins and the Mimasaka school of Kumarila Bhatt believe Anupalabdhi to be a separate independent pramāņa. Non-existence of a thing is apprehended by its non-perception. By not seeing a jar in a place one knows that it is not there. We use this method of knowledge also very often, and this is evident from statements like : ‘There is no teacher in the class-room’, There is no sound here’, ‘This flower has no fragrance’ etc. It may seem paradoxical that non-apprehension of a thing is a means to the apprehension of its non-existence (abhāva). But in fact both non-perception as well as perception serve as a means to get various knowledge, for the simple reason that the knower is conscious of both. They lead to positive & negative experiences.
Sambhavam means equivalence. When we take a vessel to an experienced cook, he can say with certainty that a particular amount of rice can be cooked in that vessel. Similarly, one hundred exists in one thousand. When such an understanding appears in the intellect, it is known as Sambhava.
Aitihyam means a traditional account. This pramāņa applies when something is known by common belief or tradition but the original source of that knowledge is unknown. For instance, the old fort in New Delhi is believed to have been built by the Pāndavas, although there is no scriptural evidence to support this belief.