What did Sigmund Freud mean when he said "the mind is like an iceberg; it floats with one-seventh of its bulk above the water"?
The quote uses the analogy of an ice berg to demonstrate that only a small portion of the mind is 'visible'.
In Freud's theories of conciousness, the concious mind is the 'tip of the ice berg'. Working, in 'layers' underneath, is the preconscious and unconscious minds.
The preconscious is responsible for recall and can be accessed via cues. For example, you usually don't actively think about your email address, but if someone asks for it, you can access that information instantly. In the ice berg analogy, the preconscious mind is just below the surface. The waves and motion of the ocean can expose these parts of the berg, but mostly it remains just out of view.
The unconscious mind underlies our base feelings and emotions. This is like the 'base of the ice berg, hidden far below the ocean'.
When Freud, the founder of psychology, said that "the mind is like an iceberg; it floats with one-seventh of its bulk above the water," he was referring the importance of the unconscious in directing human behavior. Before Freud, people were not aware of the ways in which their unconscious or subconscious minds affected their behavior. Freud saw the unconscious at work in human behaviors such as Freudian slips, in which people say what is truly on their minds in spite of their attempts to disguise or hide their feelings or thoughts. He believed dreams are also a way to access what is in the unconscious. The iceberg metaphor conveys Freud's idea that a great deal of human behavior is controlled by the unconscious—much more than the behavior controlled by conscious thoughts.
In the iceberg metaphor, the id—the term Freud used to refer to instinctual human desires driven by the pleasure principle—is the part of the iceberg submerged under the water. The superego, the part of the mind that operates according to societal rules, is the part of the iceberg that is fully above the water. The ego, the reality principle which mediates between the id and the superego, is partly above water and partly submerged, meaning it is part of the unconscious and conscious mind.