The Nyaya-sutras probably were composed by Gautama or Akshapada about the 2nd century BCE. India is often equated with spirituality, but the truth is India as a society has always dominated all the aspects of knowledge. This is because of a very sound solid logical system on which the India society is based. The foundations of this logical system are in the Nyaya school of Philosophy. So, as part of the Shat darshan that is six orthodox schools of philosophies of India, let’s go over Nyaya Philosophy. Nyaya philosophy is the base on which the higher philosophies of India have been built. 

Nyaya philosophy says that all our sufferings are dues to our ignorance, there to overcome them acquiring right knowledge is very important. As a result, Nyaya philosophy puts in a lot of emphasis on gaining the right knowledge. This is why a the Naiyayikas have worked extensively on Pramana Shashtra, where they have carefully categorized all the different forms of Pramanas (i.e. Source of Knowledge).

Nyaya epistemology accepts four out of six Pramanas as reliable means of gaining knowledge. These are:

Pratyakṣa (perception), It is of two types in Hindu texts: external (Laukik) and internal (Alaukik). External perception comes from the direct interaction of the senses with worldly objects, such as seeing, hearing, tasting etc. The internal perception arises from inner sense of the mind through our intuition.

Anumāṇa (inference), In this pramana you reach a conclusion from one or more direct observations and then applying reason based on previously known truths. A classic example for this is observing smoke and inferring that there is fire.

Upamāṇa (comparison and analogy), the best example of this is that if a person has never seen a wolf and you tell him that a wolf just looks like a German Shepherd dog but lives in wild and will be found in pack. When the person goes to a jungle and sees an animal like the German Shepherd dog and identifies it to be a wolf then he has used Upmana.

Śabda (word, testimony of past or present reliable experts): What here means is that Nyaya Philosophy believes in the authenticity of the Vedas, which is why this is considered one of the six orthodox Hindu schools of Philosophy.

Arthapatti and Anuplabdhi are not accepted as the valid source of knowledge in Nyaya Philosophy, where arthapatti is a circumstantial proof, while anuplabdhi is proof by negation.

Padārtha is a Sanskrit word that refers to “categories” in Vaisheshika and Nyaya schools of Hindu philosophy. The term is a composite of pada (word, phrase) and artha (meaning), connoting in philosophical terms “a metaphysical correlate”, or in other word categories that are different, distinct types of existent. Padartha is a word used in Hindu philosophy to describe objects that can be thought and named.

The Nyaya metaphysics recognizes sixteen padarthas or categories and includes all six (or seven) categories of the Vaisheshika in the second one of them, called prameya. • These sixteen categories are • pramāṇa (valid means of knowledge), • prameya (objects of valid knowledge), • saṁśaya (doubt), • prayojana (aim), • dṛṣṭānta (example), • siddhānta (conclusion), • avayava (members of syllogism), • tarka (hypothetical reasoning), • nirṇaya (settlement), • vāda (discussion), • jalpa (wrangling), • vitaṇḍā (cavilling), • hetvābhāsa (fallacy), • chala (quibbling), • jāti (sophisticated refutation) and • nigrahasthāna (point of defeat).

Pratyakṣa (perception) occupies the foremost position in the Nyaya epistemology. Perception is defined by Akṣapāda Gautama in his Nyaya Sutra as a ‘non-erroneous cognition which is produced by the intercourse of sense-organs with the objects, which is not associated with a name and well-defined’. Perception can be of two types, laukika(ordinary) and alaukika(extraordinary). 

Ordinary perception: Ordinary (Laukika or Sadharana) perception is of six types – visual-by eyes, olfactory-by nose, auditory-by ears, tactile-by skin, gustatory-by tongue and mental-by mind. 

Extra-ordinary perception: Extraordinary (Alaukika or Asadharana) perception is of three types, viz., 

• Samanyalakshana (perceiving generality from a particular object), 
• Jñanalakshana (when one sense organ can also perceive qualities not attributable to it, as when seeing a chili, one knows that it would be bitter or hot), and 
• Yogaja (when certain human beings, from the power of Yoga, can perceive past, present and future and have supernatural abilities, either complete or some).

The Naiyayika maintains two modes or stages in perception. The first is called nirvikalpa (indeterminate), when one just perceives an object without being able to know its features, and the second savikalpa(determinate), when one is able to clearly know an object. 

Syllogism is a method of deductive reasoning to come to a conclusion. In Indian syllogism however there are five steps

1. There is fire in the mountains (Pratigya, First Proposition)
2. Smoke is coming from there (Hetu, Second Proposition)
3. Where there is Smoke, there is fire (Udahran, Universal Proposition that is proven through Vyapti, where one thing is always associated with other, such as smoke and fire)
4. Thus, it can be perceived (Upanaya, Application of Universal Proposition in current case)
5. There is fire in the mountains (Nigaman, conclusion)

Inference Anumāna (inference) is one of the most important contributions of the Nyaya. It can be of two types: 

• inference for oneself (Svarthanumana, where one does not need any formal procedure, and at the most the last three of their 5 steps), and • inference for others (Parathanumana, which requires a systematic methodology of 5 steps).

Comparison Upamāna, which can be roughly translated as comparison is the knowledge of the relationship between a word and the object denoted by the word. It is produced by the knowledge of resemblance or similarity, given some pre-description of the new object beforehand.

Verbal testimony Śabda or verbal testimony is defined as the statement of a trustworthy person (āptavākya), and consists in understanding its meaning