The V cord is often referred to as the "dominant chord" in the I, IV and V progression. But I'm finding that the IV chord can often take on the character of "driving" the song, as if it is meant to be played harder/louder at times. Is there any consensus on this thought?
Descriptions like this can become a bit subjective and vague, but we can still try to explain what is felt.
I would suggest there are two things going on:
In common practice, "classical" harmony the standard functional progression is subdominant
IV to dominant
V to tonic
I. But in that paradigm we can also say the tonic/dominant pair is basic harmonic dynamic. In other words a huge amount of classical harmony is alternating between
V. I could be said that the motion between
V becomes almost a harmonic non-event, because it is so common. If the harmony is heavily tonic/dominant like that, when a subdominant is introduced it is pretty noticeable, and glossing over a bunch of potential detail, it sort of announces the coming dominant. That "announcing" certainly can feel like a major harmonic "driver."
The other possible explanation is a bit of classical theory combined with blues/rock style. While
IV V I is a progression that exemplifies functional progression, with subdominant to dominant to tonic representing stages of forward progress, there is another model of progress: prolongation.
Let's return to the functional progression
IV V I just for a moment and think of that forward progress in syntactic terms. It's a bit like "he kicks the ball into the goal." Each unit is connected with a certain necessity: boys kick, balls get kicked, kicked balls go into goals. Musically subdominants go to dominants, and dominants go to tonics, tonics ultimately are the end.
Prolongation also provides forward movement, but the "engine" behind it is different. Harmonically a prolongation is something like
I IV I, which would specifically be a tonic prolongation. We could say that syntactically it really reduces to
I, and the
IV is just an interposed elaboration of
Because you can reduce such prolongations they are sometimes describe in a way that makes them seem less essential, nevertheless they still provide forward progress. I suppose you could say prolongations provide elaboration detail that creates anticipation for the eventual continuation. Linguistically it's like taking the dull phrase "he kicked the ball..." and starting it with an elaboration "the boy, who was the star of the team, with all his might..." which sort of builds things up for "kicked the ball."
In a typical 12 bar blues the
IV chord works as an elaboration of
I during the first 8 bars...
I IV I I IV IV I I
When the final 4 bars of the turnaround are played...
V IV I V
...we can see the
V leading back to
I - when the 12 bars get repeated - satisfies our "functional" sense of dominant to tonic progression as a harmonic driver, but the prolongation through
IV that happens in the first 8 bars in another important harmonic driver. Imagine how static the first 8 bars would be if it were all tonic.
Your question is specifically about
I IV V and I think the "drive" created by
IV is simply the "announcing" the dominant will be coming next. But, I thought it was important to mention
IV in prolongation and it is a driver too.
Maybe there is a bigger point to make about human nature. Perhaps anticipating an event is more significant that the event itself. So,
IV is a big driver, because we savor the anticipation leading to
V. And to be very clear about our functional progressions
I is the end. Ending isn't much of a driver. So, tonic/dominant is the structural foundation, but
V is the real dynamic driver.
It's important to understand that subdominant doesn't mean "just below the tonic," but rather "equally far away from the tonic just in the opposite direction.
Key of C
F G A B C D E F G
IV. -------- I. -------- V
Notice above that (if C is the tonic) G is the dominant five steps above and F is the subdominant five steps below. The same is true for the mediant (E) and submediant (A).
In many compositions from many different periods, if one of these two (dominant, subdominant) is used extensively in a piece, visiting the other makes a satisfying ending.
Also bear in mind that The subdominant-tonic relationship in one key is the tonic-dominant relationship in another. Below, in the key of F, the F-C functions as I-V whereas in the key of C it was IV-I.
Key of F
Bb C D E F G A Bb C
IV. ---------I. -------------V
The word "dominant" is part of the "tonal system" of thinking about the functions of chords within a key. It doesn't necessarily imply anything about dynamics or volume (though you might be able to draw some generalizations about it). Its "dominant" role in a key has more to do with what its job is and how well it can do it.
The concept of tonality is built on the idea of moving away from the "tonic," the "I" chord, the "home base" of the key, and then wanting to get back to it. The dominant is the chord that most strongly sets up an expectation of the tonic coming next. Other chords in a progression are usually there just to set up the dominant (thus IV is the "predominant"), and once the dominant comes along it takes its big moment to "resolve" to the tonic. Your sense of the "driving" tension of the IV probably comes from its role in leading to the V, but it doesn't have anything to do with the evolution of the names of the chord functions.