Some people think that to assert a proposition you need to grasp it.
I think they are mistaken. Suppose my wife asks me: "Can you take the car to the garage to have xyz done to it?" I have no idea what "xyz" means. It's some complicated thing having to do with internal combustion engines. I ask her: "How long do you think it'll take them to do xyz?" She says: "It shouldn't take more than two or three hours." So I say: "OK, I'll have them do xyz." I take the car to the garage and ask them: "Could you do xyz to the car?" Two hours later they tell me: "We did xyz" and hand me a bill for $250. I call up my wife and say: "They did xyz and it cost $250."
I engaged in four speech acts where I used "xyz": a question to my wife about how long xyz takes, a promise to my wife to have xyz done, a request of the mechanic that xyz be done, and finally something that looks like an assertion that it cost $250 to have xyz done. Clearly, I asked my wife about how long xyz takes, I promised my wife to have xyz done and I requested of the mechanic that xyz be done. For it is under the supposition that I asked my wife how long xyz takes that her response that it takes an hour or two is salient, and plainly it is salient. That I promised to have them do xyz is also clear--if instead I ask them to change the oil (assuming xyz isn't in fact an oil change--the two to three hour time estimate suggests it's not), I haven't done what I promised, and I owe my wife an apology. And if I didn't ask the garage to do xyz, then they performed an unauthorized repair.
But if my apparent question, promise and request are what they seem, despite my lack of grasp of "xyz", surely the same should be said about my apparent assertion that they did xyz and it cost $250. Indeed, if instead I had the shop do an oil change, then I lied when I told my wife that they did xyz. But how could I have lied unless I asserted? Moreover, if I spoke sincerely but later a friend looked in the engine and told me: "They didn't do xyz!", then I should withdraw what I said to my wife. Again, the best explanation of why I should withdraw it is that it was an assertion that has since turned out to be incorrect.
