Practice-based philosophy of science has gradually arisen in the sociology of scientific knowledge (SSK) and science and technology studies (STS) during the past decades. It studies science as an ensemble of practices and theorising as one of these practices. A recent study has shown how the practice-based approach can be methodologically justified with reference to Peirce and Dewey. In this article, I will explore one consequence of that notion: science, as practice, is necessarily social. I will disambiguate five different senses (...) in which science is social. First, science presupposes language, which is essentially social. Second, practices, including science, are adaptations of the behaviour of an organism to an environment, of which other organisms are a part. Third, practices, including science, are public and hence shareable. Fourth, scientific knowledge can serve as a vehicle of social and moral reform. Fifth, scientific knowledge can be applied to improve the human condition. This fivefold result bears on the problem of realism. (shrink)