The Nyaya school holds that there are four valid means of knowledge: perception (pratyaksha), inference (anumana), comparison (upamana), and sound, or testimony (shabda). Invalid knowledge involves memory, doubt, error, and hypothetical argument.Nyaya school is one of the six astika schools of Indian Philosophy.This school's most significant contributions to Indian philosophy were the systematic development of the theory of logic, methodology, etc.According to Nyaya's Philosophy, nothing is acceptable unless it is in accordance with reason and experience (scientific approach). Nyaya is regarded as a logical thinking technique. Important PointsUpamana Pramana (Comparison): It is a kind of knowledge we get by the assumption of similarity between the two different types of knowledge. It is basically based on comparison and not just only perception and assumptions.For example, a person who knows a four-legged animal that barks is called a dog. Therefore, when he goes to a jungle and see a similar-looking animal he can relate that its a wild dog that has also four leg and barks.This knowledge is possible when there is an earlier similarity with a particular thing which helps the person to compare both the similar things.Hence according to the Ny?ya school, the given argument exemplifies Upamana Pramana (Comparison) Additional InformationSabda (Verbal Testimony ): This is mainly through verbal indication. We get a lot of knowledge through verbal statements, symbols, texts, or words. A verbal statement must have a valid cause for its information to be true.Arthpatti (Postulation): Arthapatti Pramana, we understand the knowledge which we get through the relation and its implications. It includes supposition, belief, and presumption.We get this type of knowledge either from what we have seen or heard and by pure assumption.Anumana (Inference): Here the knowledge is gained not through any sense organs but through anumana or assumption. We assume knowledge of what we dont see from what we see.