A construct in the philosophy of science is an ideal object, where the existence of the thing may be said to depend upon a subject's mind. This contrasts with a real object, where existence does not seem to depend on the existence of a mind.
In a scientific theory, particularly within psychology, a hypothetical construct is an explanatory variable which is not directly observable. For example, the concepts of intelligence and motivation are used to explain phenomena in psychology, but neither is directly observable. A hypothetical construct differs from an intervening variable in that it has properties and implications which have not been demonstrated in empirical research. These serve as a guide to further research. An intervening variable, on the other hand, is a summary of observed empirical findings.
The creation of constructs is a part of operationalization, especially the creation of theoretical definitions. The usefulness of one conceptualization over another depends largely on construct validity. To address the non-observability of constructs, U.S. federal agencies such as the National Institutes of Health National Cancer Institute has created a construct database termed Grid-Enabled Measures (GEM) to improve construct use and reuse.
Concepts that are considered constructs by this definition include that which is designated by the symbol "3" or the word "liberty". Scientific hypotheses and theories (e.g. evolutionary theory, gravitational theory), as well as classifications (e.g. in biological taxonomy) are also conceptual entities considered to be constructs.