I don't think we have anything else *but* subjectivity. If I can
   correlate my *grid of reality* to equivalent concepts in your
   "grid of reality" - then we appear to have agreement.

   If a whole BUNCH of people do it, then we have languages,
   systems, sciences, common beliefs, cultures, stereotypes, etc.

   It's hard to "be yourself" and trust your own grid. It's far
   easier to trust other people's and use theirs - and we do.
   Besides, agreement squirts out positive emotional chemicals in
   the brain and we humans seem to like that drug.