Music Theory : I or i, IV (or iv, or ii or II), V (quora)

Q

What is the difference between tonic, subdominant and dominant in music?
https://www.quora.com/What-is-the-difference-between-tonic-subdominant-and-dominant-in-music/answer/Hans-Georg-Lundahl

Hans-Georg Lundahl

Self Employed at Writer and Composer

Answered just now

• The tonic is the home chord of a composition (the one a Schenkerian analysis will reduce it to), which is stated or implied at the end - same applies to any phrase in it, since these are minor compositions too, it is also its base note;
• The dominant is one fifth above the tonic, is a major chord, and is the usual chord just before the home chord at the end of a phrase or composition : the reason for its usually being major is that the major third of the dominant is a leading note, leading up to the tonic note;
• The subdominant does not have a set function, but can replace the dominant in the cadence, thus making it a plagal one, its base note being a leading note to the major third (if such) of the tonic, it can also prepare the dominant, but can also in both capacities be replaced by a major or minor double dominant. It is, essentially, an intermediate.

You can end a composition on tonic in full cadence, or just before tonic, on dominant, in half cadence (meaning you imply, but refuse to actually state the tonic), but you can not very well end it on either subdominant or double dominant, these feeling a bit too intermediate. Transposing a whole phrase that way is another matter, in that case the original subdominant or double dominant of the composition has become the new tonic of the final part of it.

[I am, like some of the other answers, assuming the questioner already can find these on a scale. I am however also more treating them as conventional functions in musical composition rather than as just places in the scale.]