It's not just questions of language or rhetoric. Do computers exist, yes. Do people exist, yes. Does god exist, cant answer that one. Does a creature made of shit and arms and legs that eats peaople to survive and is as big as a building exist, no.
Life is yes or no.
Reality is yes or no. It seems as though Toulmin's central idea hinges on mere matters of communication and terminology. The existence of something shouldn't be predicated on how we talk about it or if its descriptions are theoretical. Similar to the God example used, it seems that the author is trying to say we can't say for sure whether electrons exist. That does not mean that we have to stop being critical of science.