The first three acts of Julius Caesar exemplify Shakespeare’s interest in depicting the material outcomes of affect and cognition within a densely realised world where social intimacy forms the basis for political decision-making. This essay concerns moments of inter-subjective inference when characters reveal the conditions of affective community. It argues that Shakespeare is interested in how patrician Romans think they know one another deeply because they share the self-conscious, public history central to romanitas. He shows us how the affective community thus formed is destroyed by factionalism and metaphorical language when metaphor replaces the practical language of social knowing and participates in the breakdown of community. This power of metaphor becomes clearest in 2.1 when Brutus decides to kill Caesar by comparing him to an adder. The metaphor shows social cognition betraying its own best uses when Brutus metaphorically casts out a known, loved fellow being from the human community in order to make him politically a thing you feel obliged to kill.