Instincts: strong innate forces that provide all the energy in the psychic system. Freud"s original theory of instincts was influenced by darwin"s theory of evolution. In initial formulation, two instincts classes: self-preservation instincts, sexual instincts. In later formulations, freud collapsed self-preservation and sexual instincts into one, called life instinct (libido); added death instinct (thanatos) Although freud initially believed that the life instinct and death instinct worked to oppose one another, he later argued that they could combine in various ways. Unconscious motivation: sometimes we don"t know why we do what we do. Part of the mind holding thoughts and memories about which person is unaware. Includes unacceptable sexual and aggressive urges, thoughts, and feelings. Freud argued that nothing happens by accident - instead there is a reason behind every act, thought, and feeling. Everything we do, think say, feel is an expression of our mind - either conscious, preconscious, or unconscious.