Recently, sociologists have expended much effort in attempts to define social mechanisms. We intervene in these debates by proposing that sociologists in fact have a choice to make between three standards of what constitutes a good mechanistic explanation: substantial, formal, and metaphorical mechanistic explanation. All three standards are active in the field, and we suggest that a more complete theory of mechanistic explanation in sociology must parse these three approaches to draw out the implicit evaluative criteria appropriate to each. Doing so will reveal quite different preferences for explanatory scope and nuance hidden under the ubiquitous term "social mechanism." Finally, moving beyond extensive debates about realism and antirealism, we argue prescriptively against "mechanistic fundamentalism" for sociology and advocate for a more pluralistic understanding of social causality.