A commonly held view among scientific realists (e.g., H. Sankey) is the view ascribing common sense the twofold role of grounding science in the empirical world and providing it with an evolutionary justification (the genetic priority thesis), on the one hand, and of laying the original epistemic foundation upon which the building of science rests (the epistemological priority thesis), on the other hand.
But what exactly is common sense? I will argue there are (at least) two answers to this question, quite distinct, but prima facie equally plausible. I will argue further that the answer that tends to be favoured by scientific realists is actually the one that is most unsuitable for vindicating either the epistemological priority thesis or the genetic priority thesis. I will conclude by considering how endorsing the less favoured answer could actually lead us to envisage how to satisfy these desiderata.