Water is not H 2 O
What makes a liquid water? A strong version of ``psychological essentialis'' predicts that people use the presence or absence of H2O as the primary determinant of what liquids they call ``water.'' To test this prediction, subjects were asked to judge the amount of H2O in liquids called ``water'' and liquids not called ``water.'' Neither their beliefs about the simple presence/absence of H2O nor about the proportion of H2O in the liquids accounted well for which ones are normally called "water." Typicality ratings and an extended tree solution on similarity ratings suggested that use, location, and source of a liquid may also influence whether it is considered to be water. Sentence acceptability judgments further suggested that there may be a sense of "water" that corresponds to the strong essentialist view, but that there is also a more general sense in common use encompassing mixtures with varying amounts of H2O. These findings indicate that essentialist beliefs alone may not fully explain category membership judgments and word use, and they suggest a modified version of psychological essentialism.