What are the problems between the grammatical principle and the other two principles?

What are the problems between the grammatical principle and the other two principles?

Problems arise through occasional conflict between the grammatical principle and the other two principles. The notional principle, as the name suggests, is concerned with the subject-verb concord on the semantic basis, i.e. according to the notion of number rather than the physical presence of the grammatical marker of that notion. Such a concord is especially common between a verb and its subject that contains a collective noun. Whether plural or singular depends to a large extent on the speaker’s understanding of what such a noun refers to, e.g., to a group of people as a whole or as individuals.