Hinduism teaches that for as long as we are imperfect beings, we cannot discern the truth from falsehood with 100% certainty. All we can do is our best. But Hinduism does provide guidelines for this.
There is a Sanskrit term, Pramana (प्रमाण, Pramāṇa), meaning ‘proof’ or ‘means of knowing truth’. Pramana interacts with Pramatra (प्रमातृ, Pramātŗ, the knower) and Prameya (प्रमेय, the known), which are equally important parts of the knowledge process, since their own characteristics influence the knowledge.
Ancient Hinduism identified six Pramanas. The various schools of Indian philosophies further categorize each of the six Pramanas in terms of conditionality, completeness, confidence, and possibility of error. They are:
- Pratyaksha (प्रत्यक्ष), perception: what you yourself directly perceive to be true. This is the only one held by the Charvaka school of Hinduism to be a reliable source of knowledge. It is subdivided into external perception (the interaction of the physical senses and external objects) and internal perception (the inner senses within the mind, including pratibha or intuition, samanyalakshana or induction from perceived specifics to a universal archetype, and gnyanalakshana, the perception of a thing’s previous state by observing its current state). To ensure the reliability of perception, you must have indriyarthasannikarsha (direct experience by one’s sensory organ(s) with the object), avyapadeshya (non-reliance on hearsay or someone else’s perception), avyabhichara (consistency of the perception over sustained observation), and vyavasayatmaka (care to observe all details, not mix inference with observation but keep them separate and sequential, and consciously ensuring that you are not just observing what you want to observe or not observing what you do not want to observe). There is also extra-ordinary (alaukika or asadharana) perception, which includes Yogaja, when through the power of Yoga supernatural perceptions are possible.
- Anumana (अनुमान), inference: what you do not directly perceive, but can infer to be true based on applying reason to what you did perceive. The classic example is perceiving smoke and inferring fire. These first two are the only ones held by the Vaisheshika and Buddhist schools to be reliable means of knowledge. Anumana consists of pratignya (hypothesis, consisting of sadhya or the idea to be proven or disproven and paksha, the object on which the sadhya is predicated), hetu (the reasoning to prove the hypothesis, which must separately account for the inference in all cases, why the hypothesis is true in cases when it applies, and why it is not true in cases when it does not apply), and drishtanta (examples, of which sapaksha, positive examples, must be present and vipaksha, negative examples, must be absent). All this can lead to a nigamana, or conditionally proven conclusion.
- Shabda (शब्द), testimony of reliable experts: what you hold to be true because reliable experts told you it is true. This is inevitably the primary source of knowledge for any human, since a human has finite time and energy and can learn only a tiny fraction of facts and truths directly. These first three are the only ones held by the Sankhya, Yoga, Dvaita Vedanta, Vishishtadvaita Vedanta, and Jain schools to be reliable means of knowledge. The problem, of course, is establishing the reliability of a source. Indeed this is impossible for a human to do beyond any doubt.
- Upamana (उपमान), comparison and analogy: what you can infer to be true based on its similarity with other things which you hold to be true. These first four are the only ones held as acceptable by the Nyaya school. A classic example is a man who has never visited a land where a certain animal lives. He or she is told, by someone who has been there, that in that land there is an animal that sort of looks like a cow, grazes like a cow, but is different from a cow in such and such a way. Such analogy and comparison may help you to identify the new animal later. Upamana is divided into thirty-two types, of varying value and reliability.
- Arthapatti (अर्थापत्ति), postulation or derivation from circumstances, similar to circumstantial implication. For example, if a person left in a boat earlier, and the time is now past the expected time of arrival, then it may be reasonable to postulate that the person has arrived. This is at best a weak Pramana, because the boat may have gotten delayed or diverted. It is more reliable in the case of deriving the time of a future sunrise or sunset. Another example is : Devadatta is fat, but Devadatta does not eat during the day; therefore Arthapatti implies that Devadatta eats at night. These first five Pramanas are accepted by the Prabhakara Mimansa school.
- Anupalabdhi (अनुपलब्धि), non-perception: what you conclude is true or not true based on what you did not perceive. The classic example is “there is no jug in this room”, since you can clearly see the whole room and there is no jug. This is categorized into non-perception of cause, non-perception of effect, non-perception of object, and non-perception of contradiction. This is considered a last-resort Pramana even by those schools which accept it, which include Bhatta Mimansa and Advaita Vedanta.
Several more Pramanas exist in various schools, but are less emphasized.