This overview of active inference offers an account of embodied exchange with the world that associates neuronal processing with inferring the causes of our sensations. Its agenda is to link formal (mathematical) descriptions of dynamical systems to a description of active perception in terms of beliefs and goals. The argument has two parts: the first calls on the lawful dynamics of any (weakly mixing) ergodic system– from a single cell organism to a human brain. These lawful dynamics suggest that (internal) states can be interpreted as modelling or predicting the (external) causes of sensory fluctuations. In other words, if a system exists, its internal states must encode probabilistic beliefs about external states. Heuristically, this means that if I exist (am) then I must have beliefs (think). The second part of the argument is that the only tenable beliefs I can entertain about myself are that I exist. This may seem rather obvious; however, it transpires that this is equivalent to believing that the world – and the way it is sampled – will resolve uncertainty about the causes of sensations. I will conclude by looking at the epistemic behaviour that emerges under these beliefs, using simulations of navigation and (saccadic) searches.