The aim of the paper is an attempt to show the relationships between two main contemporary theories of psychological mechanisms of placebo action: classical conditioning and expectancy.Two main contemporary theories of psychological mechanisms of placebo action are presented: classical conditioning and expectancy. The relationships between them are discussed. Arguments are presented for the thesis that the theories does not exclude each other but the range of phenomena they explain is not completely the same. Conditioning involves either conscious learning (acquiring and changing expectancies) or unconscious learning (conditioning not mediated via expectancies). Expectancies are always potentially consciously accessible. They can be acquired and changed by both conditioning and other procedures, for example verbal information. Summing up, either conscious learning (expectancy and conditioning) or unconscious learning (conditioning) can be the mechanism of placebo action.
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