2021-03-192021-03-192020-04-24McGann, M. & Speelman, C, P. (2020) 'Two kinds of theory- what psychology can learn from Einstein', Theory and Psychology, 30(5), 674-689.https://dspace.mic.ul.ie/handle/10395/2951A century ago, Einstein distinguished between two kinds of theory—theories of principle and constructive theories. These have separate but complementary roles to play in the advancement of knowledge, in the manner in which they relate to data and in how they are developed. The different kinds of theory carry implications for what kinds of data we produce and for how they are put to use. We outline Einstein’s distinction and the model of theory formation that it involves. We then use the distinction to look at some of the discussion of scientific practice in psychology, particularly recent work on the need for more theoretical, rather than purely methodological, sophistication. We argue in agreement with Einstein that the distinction is a useful one and that adopting it as a tenet of theoretical development requires a renewed commitment to a natural history of psychology.enghttps://journals.sagepub.com/doi/10.1177/0959354320937804https://journals.sagepub.com/Scientific practiceTheories of principleConstructive theoriesNatural historyExploratory researchArticle10.1177/0959354320937804