[kreyenborgi]

If you simply want to ground statements in statements, you quickly get into GOFAI territory where you need to build up the full semantics of a sentence (in all supported languages) in order to prove that two sentences mean the same or have the same denotation or that one entails the other.

Otherwise, how do you prove the grounding isn't "hallucinated"?

[mattigames]

The root issue is that us humans perceive our own grasp on things better than it is ( "better" may be the wrong word, maybe just "different"), of how exactly concepts are tied to each other in our heads, it's been a primordial tool for our survival, and for our day to day lives but it's at odds with the task of building reasoning skills in the machine, because language evolved first and foremost to communicate among beings that share a huge context, so for example our definition of the word "blue" in "the sky is blue" would be wildly different if humans were all blind (like the machine is, in a sense)