Earlier quoted context omitted.
That's pretty good. But then knowing that ambiguity, I could craft a statement like, "I walked a mile on the treadmill today."
Exactly, and if you keep going, you'd notice you need each time a longer, more precise description, which at the same time, paradoxically, opens the door for more ambiguity. In that example, the first context is English language, then knowing who I is, then what a mile is, and a treadmill and today. All of those are contextual. Even mile. How long is a mile? Like any physical measure, it actually varies, because it i…
> the first context is English language
Let's ignore this context. If you don't understand English then you shouldn't be expected to understand an English statement regardless of context.
> How long is a mile?
That depends on what time and space you are in. But that's ok. All such measurements are relative and defined by non-natural constructs. But we can be realistic and assume a mile is whatever our government has decided.
When I tell you "I ran a mile", I'm not telling someone in Australia I ran a mile. I"m telling you that. If we are speaking over the internet it might complicate things, but we only have to resolve the meaning of mile once for our relationship, and all proceeding discussions will use this meaning.
I would argue that this makes the word mile unambiguous in the sense that you are saying. If we had to assert each time what I meant by a mile, then that would be ambiguous.
> that sentence might not make any sense to someone reading it in 20 years
Evolution of language is a separate phenomenon. We don't need to consider that. Only what the language means today right now as I use it. That's the utility of language. For older English texts, we have literature which matches our common vernacular to the vernacular of the time. Foreign translations are out of scope for the same reason listed above. Since we have mappings between today's English and yesterday's English, I would again argue that this is not a source of ambiguity.
> And then when is today? May 7, 2019
That doesn't have anything to do with language. That is a chronospacial coordinate. It represents a certain degree of completion of our orbit around the sun. It isn't a measurement of time at all. It's only relative in the sense that all time and space measurements are relative to the spacetime coordinate of the Big Bang.
Time is inherently a relative concept. We don't have time unless we are comparing (relating) two different frames. We define one in terms relative to the other (motion, state, etc). In a single, non-relative frame of reference time just doesn't exist.
> And then finally, what if you were lying?
Again, this has nothing to do with language. You aren't trying to guess what I'm thinking, you're trying to understand what I'm saying. That's what language parsing is about. Discussion of motivations, misdirection, etc. is irrelevant.