Can what we know change what we see? Does language affect cognition and perception? The last few years have seen increased attention to these seemingly disparate questions, but with little theoretical advance. We argue that substantial clarity can be gained by considering these questions through the lens of ‘predictive processing’, a framework according to which mental representations—from the perceptual to the cognitive—reflect an interplay between downward-flowing predictions and upward-flowing sensory signals. This framework provides a parsimonious account of how (and when) what we know ought to change what we see, and helps us understand how a putatively high-level trait such as language can impact putatively low-level processes like perception. Indeed, within predictive processing, language begins to take on a surprisingly central role in cognition by providing a uniquely focused and flexible means of constructing predictions against which sensory signals are evaluated. Predictive processing thus provides a plausible mechanism for many of the reported effects of language on perception, thought and action, and new insights on how and when speakers of different languages construct the same ‘reality’ in alternate ways.