To further the understanding on the mechanism of numerical scale values, this study varied the numerical labels for scale points and examined its effect in relation to individual respondent’s need for cognition. Embedded in a web survey, this experiment succeeded in producing a variety of evidence that respondents worked out an inference from the numerical values and based their responses on that inference. The shift in responses induced by the numerical scale values wasunexpectedly robust; when a scale started with a negative number, it pushed the responses to the right or the positive end of the scale across items and across fonts. Process measures (such as recall) and answers to the retrospective probe confirmed that respondents paid attention to the numerical labels on the scales and used them to interpret the verbal labels on the end points of the scale. However, not everyone was affected by the numbers on the scales. The hypothesized effect of the negative scale values was observed only among respondents with a high need for cognition, but not among those with a low need for cognition. This finding seemed to suggest two things. First, Gricean effects of this sort involve controlled processes; people need to process deeply for the numbers to affect the answers. Second, unlike the response errors committed by satisficing respondents (who skip or slack off on certain cognitive steps), Gricean effects are an optimizing error or high effort error, committed by respondents who try to be good, cooperative, and thorough respondents.