That distinction is a matter of whether the law is a prescriptive statement (don't murder anybody) or a descriptive statement (water boils at 100°C). Prescriptions and descriptions are both products of human brains. It's just nitpicking on my part; in the end, it's true that water boils at 100°C, whether we interpret that statement as an inherent property of water or a verbal elucidation of some observed pattern. I prefer to think of it the second way, because if you say laws are real things that are part of the universe, it's strange that we can't find them anywhere in the universe. I'm not saying reality depends on someone looking at it or anything so esoteric, just that the particular ways humans parse reality into sentences that capture aspects of it should not be mistaken for a fundamental underlying reality, which we don't have access to although we have good reason to suppose it exists.
Sentences are human dependent. The actual expressing of a sentence is human dependent.
Not really, no.
An artificial intelligence designed in another galaxy by some utterly alien civilisation could conceivably invent and use the same language as we do. Very unlikely of course but logically possible since it would in fact be a matter of sheer probabilities. Much less probable than 1/52! but still logically possible. Nothing metaphysical about that.
That which is expressed, however, is a statement, and though statements made by humans require human beings, a statement is often considered not to be much unlike a proposition which does not in any way shape or form require a human.
A statement can just as well be the sentences uttered or the supposed meaning motivating these sentences. Either way, a statement is as profoundly human as any sentence in a human language is since if it's understood as referring to the possible meaning, the meaning in question is always one inferred by one human being or another. And different meaning may well be inferred by different human beings, so the notion that a statement is like a proposition gets into the same kind of trouble as sentences do, namely that there will always be an embarrassing multiplicity of them.
And, the term "proposition" originally just means the act of making known your intention, very similar to "statement" and "sentence", and again something profoundly human if performed by a human. It's only rather recently that people have started to invent a new concept of proposition with the increased reliance on formal expressions in philosophy, the sciences, maths, and logic.
More importantly, the view you defend here is highly metaphysical. There's no objective evidence of any proposition in this latest sense. All that we have is our subjective experience and our belief that there's an external world corresponding to it. So the educated guess is that propositions are just idealised versions of what we mean when we utter sentences, i.e. make statements, and that the metaphysically inclined will try to make hay out of it. Your notion of proposition does no job that a rational view of mankind cannot do without using it.
The sentence, "water boils at 100C" did not exist before humans come to exist, so such a sentence at such a time before man could never have been uttered, but the proposition that would have been expressed during a time when there were no humans had there been humans to express it is true independent of a human to express such a sentence--precisely because propositions are atemporal. Although the distinction between a sentence and a proposition is great, the divide between a proposition and a statement is less enough and similar enough to regard statements as propositions in this context.
Again, it's logically possible that an alien species or an AI inadvertently visiting the Earth before mankind could come up with the very sentence "water boils at 100°C" to mean that water boils at 100°C. No big deal. The reason is that the fact that water boils at 100°C would have been true before human beings could see for themselves how hot is boiling water. So what was true then is not some metaphysical proposition but the fact itself, and this interpretation is just so much more economical and razor-like and Occam-friendly.
EB
