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This paper examines the effects of perspective taking on grammar and the processing of sentences. The perspective hypothesis claims that language allows us to shift perspective on four cognitive levels. The specific claims are that: 1. Perspective taking operates online using images created in four systems: direct experience, space/time deixis, plans, and social role taking. 2. Language uses perspective taking to bind together these four imagery subsystems. 3. Grammar arose as a social convenience to support accurate tracking and switching of perspective. 4. Language comprehension and production use both depictive and enactive imagery. Depictive imagery relies on the ventral image processing system, whereas enactive imagery relies on the dorsal system for perception-action linkages. Perspective taking depends primarily on processing in the dorsal stream. 5. On the level of direct experience, perspective shifting depends on imagery grounded directly on body maps. 6. On the level of deixis in space and time, perspective shifting depends on the projection of the body image across egocentric, allocentric, and geocentric frames. 7. On the level of plans, perspective shifting in the transitivity system assigns roles to referents through the transitivity system. Premotor working memory areas and inferior frontal action planning areas provide the processing capacity to control perspective shifts in action chains. 8. On the level of social roles, perspective switching through speech acts allows us to construct images of social reality. Switching of social perspectives is facilitated by a functional circuit including prefrontal cortex and medial structures. 9. By tracing perspective shifts in language, children are able to learn the cognitive pathways and mental models sanctioned by their culture. 10. The emergence of language as a species-specific human skill depends on a series of gradual evolutionary adaptations that supported perspective taking in the four subsystems, as well as additional adaptations for vocal control.