Is this sentence correct:
1-What I am saying is as true as the earth rotating on its axis.
(Meaning: What I am saying is as true as the statement: "The earth rotates on its axis".)
If I'm not incorrect, the consensus among our experts is that Sentence 1 is not, in fact, correct. I agree. My own reasoning is as follows.
"What I am saying is as true as..." requires some kind of noun phrase (or what Raymott ably calls a "proposition.")
Such a phrase might be "the rotation of the earth on its axis."
Hence, "What I am saying is as true as the rotation of the earth on its axis."
Why is this? To my mind it requires a something.
"the earth rotating on its axis" is very different from "the rotation of the earth on its axis." As is often the case, I'm not sure what the technical difference is, but perhaps you can understand what I am trying to say.
That may not be the best way to say it, but it does stay closer to the original form of the sentence.
But perhaps can explain more precisely what the grammatical rules are for such a sentence.
Thanks for bringing it up!