(chemistry) any theory in which all matter is composed of tiny discrete finite indivisible indestructible particles; "the ancient Greek philosophers Democritus and Epicurus held atomic theories of the universe"
(psychology) a theory that reduces all mental phenomena to simple elements (sensations and feelings) that form complex ideas by association
any personal belief about how to live or how to deal with a situation; "self-indulgence was his only philosophy"; "my father's philosophy of child-rearing was to let mother do it"
the rational investigation of questions about existence and knowledge and ethics