phrase breakdown by SEs?

how are individual words in a meta keywords phrase handled

[Clair]

I'm curious as to how the SEs treat individual words in a keyword phrase that appears in the meta keywords section.

For example, if you have a phrase like "guitar scales" or "bass lessons", "learn guitar scales" are the individual words within the phrase treated as individual words would be, or is it necessary to repeat them, as in

. . .keywords="learn guitar scales, guitar, scales">

Thanks.