"take it as read that he's actually here"

A variation on George Berkeley's theory of immaterialism or subjective idealism: "esse est percipi" (to be is to be perceived).

In his work A Treatise Concerning the Principles of Human Knowledge Berkeley posits the idea that "surely there is nothing easier than for me to imagine trees, for instance, in a park and nobody by to perceive them. The objects of sense exist only when they are perceived; the trees therefore are in the garden no longer than while there is somebody by to perceive them."

This is more often rendered as the hypothetical question: "if a tree falls in an empty forest with no one present to witness it, did it really make a sound?"