Terry's analogy of the 'free-willed light switch' attempts to reduce the concept of free will to someone doing something that their master finds to be undesirable. Supposedly humans have free will but animals do not. Anyone who has owned a cat knows otherwise.
Terry does correctly point out that we really do not have free will in a complete sense, since our options are bound by physical laws.
Our thoughts and actions are bound by preset biological processes and the concepts that we are introduced to. Free will may therefore be defined as an appearance of randomness due to an abundance of unknown factors. If the exact state of a person's biochemistry (which intrinsically includes their memories and perceptions) was known, their actions could be predicted as precisely as can astronomers predict where a planet will be a hundred years from now.