A psychologist or scientist who studies behavior from the behaviorist perspective and believes behavior is shaped by external environment rather than internal factors.
From behaviour + -ist (suffix meaning 'one who practices' a particular system or doctrine). The -ist suffix comes from Greek and Latin.
Famous behaviourists like John Watson and B.F. Skinner claimed they could explain all human behavior through stimulus and response, which seems extreme now, but in the 1920s-1950s it was thrillingly scientific and freed psychology from the murky world of introspection.
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