Primary deficit models were formulated in a context where autism was almost universally seen as an impairment. The ‘Theory of Mind’ (ToM) explanation of autism allowed researchers to make clear cuts between what appeared to be very similar behaviours — ‘carving nature at the joints’ according to a precise theory about the underlying cognitive ‘bone structure’. The ToM model of autism became extremely influential in autism research and continues to be a central component of a lot of teaching and training about autism. As well as problems with the universality of mentalising difficulties in autism, it has also been suggested that ToM difficulties are found in other groups apart from autism. The originators of the ToM account set themselves a high bar by setting out to identify a primary deficit. Mentalising skills have been associated with other early developmental milestones, such as attending to people, joint attention with others, imitation and recognising emotions.