Here's Soma by The Strokes. If I'm not mistaken, the verse progression moves simply from a G chord to an F chord repeating. If the key is C, then this is just V-IV-V-IV etc. Since the chords are only moving by step, there is no interesting root movement, (descending fifth or ascending forth, for example) yet there is still something nice about the sound. Additionally, there aren't any common tones between the IV and V chords, so the voice leading isn't crazy smooth or anything. Why does this work?
As Laurence correctly says, the song is really in G Mixolydian. It uses the same notes as C major (including an F♮), but with G as tonic, it's definitely G Mixolydian. As such, this G to F to G switch is best understood as
Explaining why it works is a bit trickier.
Let's think about "classical" music first. In this repertoire, chord progressions of an ascending step are pretty common.
I often moves to
iii often moves to
IV moves to
V moves to
vi. But chord progressions by descending step are pretty uncommon. Indeed, the only common descending-step progression is
vi moving down to
V, but even that is relatively rare and only present under particular circumstances.
But then comes popular music, and descending-step progressions are all over the place.
I loves to move to
♭VII, then that
♭VII can move to
♭VI, then that
♭VI can move to
V, and then that
V can move to
IV (!). (Let's not even talk about
The point is that it works because it happens all the time in popular music. Perhaps it's ease of playing, since we can often just shimmy our hands two frets down the guitar neck. But ears are so accustomed to this progression that we don't question it; it's as basic to popular music as
IV–V is in the Classical style.
Yes, it's the notes of the C major scale. But it's pretty obviously centered on the G major chord. Listen to the ending. That's definitely a tonic chord, isn't it! So we need a 'theory' that allows a G chord and an F chord without being 'in the key of C'. We could label it as 'G Mixolydian'. Quite common in pop music, as well as historically.
But that just labels it. It doesn't tell us WHY it works. And that can be a hard question. Sticking to one scale 'works'. But mixing scales 'works' as well. Moving by step 'works'. But so does moving by fourths, fifths, minor thirds...
Welcome to 'theory' as a descriptive art, not a prescriptive one. 'Theory Describes, It Does Not Command'. Add this to your list of 'things that sound good'. Discard any 'theory' that tells you it shouldn't.
Two Consecutive Major Chord can be only IV and V. Thus the tonic here must be C.
A bold guess but if you would transcribe the melody it would be in C major.