The present paper seeks to correct the inconsistencies of the three terms: (i) "elasticity of substitution" (ES), (ii) "substitution curve" (SC), and (iii) "marginal rate of substitution" (MRS). Such inconsistencies persist since their introduction in the 1930s. The correction of such inconsistencies can be executed in terms of Konar's (2009, 2012) "isoquant substitution curve" (IQSC) and "isocost substitution curve" (ICSC).

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