Putnam's brain in a vat argument has also been criticized. Crispin Wright argues that Putnam's formulation of the brain-in-a-vat scenario is too narrow to refute global skepticism. The possibility that one is a recently disembodied brain in a vat is not undermined by semantic externalism. If a person has lived her entire life outside the vat—speaking the English language and interacting normally with the outside world—prior to her "envatment" by a mad scientist, when she wakes up inside the vat, her words and thoughts (e.g., "tree" and "grass") will still refer to the objects or events in the external world that they referred to before her envatment. In another scenario, a brain in a vat may be hooked up to a supercomputer that randomly generates perceptual experiences. In that case, one's words and thoughts would not refer to anything: semantics would no longer exist and the argument would be meaningless.