The TIME IS SPACE metaphor consists in the use of a spatial mental time line (either left-right or front-back) to represent time. One of the issues still to be resolved is whether these space-time mappings can be automatically activated independently from the goals of the task. Prior attempts to settle this issue have failed to match adequately the temporally relevant and irrelevant tasks. In the present study we presented Spanish verbs and nonverbs conjugated in past and future forms in both a time judgment and a lexical decision task. Results showed that the left-right space-time mapping is only active when the task requires temporal discrimination, speaking against an automatic activation of the mental time line.