‘Matsya Nyaya’ literally means ‘Law of Fish’. It is the fundamental law of nature that small fish become prey to big fish or the strong devour the weak. It can be equated to the ‘Law of Jungle’. In simple words, the strong will prevail over the weak.
In absence of government or rule of law, the human society will degenerate into state of anarchy in which stronger will destroy or exploit the weak much like how bigger fish eat smaller fish. So, according to this, the theory of government was based on a belief in the innate depravity of man. In other words, this theory proposes that government, rulers and laws are necessary to prevent this natural law of ‘Matsya Nyaya’ from operating in human society.
‘Matsya Nyaya’ explains why we need to have a government and laws in place. Kautilya used this theory also to describe why a state should enhance its size and security.
According to Kautilya size enhances security, the objective is to consolidate one’s strength at the expense of other powers because given the absence of an overriding international body of law that ensures every king’s right to exist, irrespective of size, the vijigishu (King) is truly living in a system of Matsya-Nyaya, a system in which it is every man for himself. This can also be related to the modern theory of international relations known as Neo-Realism.