Vaisheshika is one of the six major schools of Hindu philosophy, founded by the sage Kanada. It is based on the concept of atomistic realism, which holds that the ultimate reality of the universe is made up of discrete, indivisible particles called atoms. These atoms are the building blocks of all matter and are eternal, infinite in number, and constantly in motion.

The main principles or tenets of Vaisheshika's atomistic realism can be summarized as follows:

1. Theory of atoms: According to Vaisheshika, atoms are the fundamental units of reality and are the smallest indivisible particles that make up all matter. They are eternal and indestructible, and their properties determine the nature of the objects they form.

2. Substance theory: Vaisheshika believes in the existence of six fundamental substances - earth, water, fire, air, ether, and time. These substances are made up of different combinations of atoms and are the basis of all material objects.

3. Law of causation: Vaisheshika holds that every effect has a cause, and every cause has a specific effect. This cause and effect relationship is known as the law of causation or karma. It is believed that the actions of individuals in their past lives determine their present circumstances.

4. Theory of perception: According to Vaisheshika, perception is the means of knowledge through which we gain knowledge about the external world. It is based on the interaction between the senses and the external objects. This theory also includes the concept of inference and testimony as valid sources of knowledge.

5. Theory of time and space: Vaisheshika holds that time and space are absolute and infinite, and they are considered as substances in themselves. Time is seen as a continuous flow, while space is seen as a three-dimensional extension.

6. Rejection of God: Unlike other Hindu schools of thought, Vaisheshika does not believe in the existence of a supreme being or God. It holds that the universe is governed by natural laws and does not require a creator or controller.

In conclusion, Vaisheshika's atomistic realism is based on the belief that the universe is made up of discrete, indivisible particles called atoms, and these atoms are the ultimate reality. The school also emphasizes the importance of causation, perception, time, and space in understanding the nature of reality. It rejects the concept of a supreme being and holds that the universe is self-sufficient and self-governing.