1> Level words>> Eg, prA's use of a word is not always the same with that of prB.  Is the definition of word 'language' the same with that of Random House Dictionary?  Not at all.  Maybe prA's definition of 'language' is bigger than that of prB.  Or the contrary.
2> Level sentence>> A sentence is built up of, in very short, <S+V+O>.  Three elements.  Given the word for S has four kinds of definition in prA's thinkings, And in prB's thinkings five.  Skip V.  Given the word for O has five in prA's and in prB's seven.  The sentence related by prA is more narrower receiived, at least so in possibility, than the same sentence, which is quite the samely built up just the same words, related by prB.
3> Psychology or Linguistics?>> This is not a problem of psychology; we say just in the world of the linguistics.  No, not the mood of prA and prB.  The language itself has within itself such problems.