Corpuscularism is a philosophical term that refers to the belief that everything is composed of small particles or corpuscles. Synonyms for corpuscularism include atomism, particulate theory, and particle theory. These terms all describe the idea that matter is made up of tiny, indivisible units. Another related term is materialism, which is the belief that physical matter is the only reality and that mental or spiritual phenomena can be explained in terms of physical properties. While corpuscularism has been influential in the fields of physics and chemistry, it has also been challenged by competing theories such as wave theory and quantum mechanics.