Can dominant chords be specified independently of a tonic (of a key)? [duplicate]

Question

The dominant chord is defined in relation to the (5th) scale degree on which it is built. This definition can often be found alongside other chord types, such as the major triad, whose definition merely (I think) specifies its internal pitches ({0, 4, 7} in integer notation).

It seems to me one can talk of a major/minor chord just based on those internal pitch relations of its own constituent notes, without reference to the context in which it appears (e.g. the key), whereas to talk of a dominant chord requires (does it not?) a further specification of a key or cadence in which said chord functions as the V.

Is it, in fact, the case that indeed "dominant chord" presupposes a key (relative to which the given chord functions as V)? If so, why are dominant chords discussed in (apparent) isolation of a functional harmony, just as a chord type?

Or is it in fact the case that a key assumption is always (at least tacitly) present, even when one just talks of a plain major chord? If so, then the apparent paradox is that the dominant chord is of course (assuming it has no added seventh) itself a major chord.

Answer 1

I think the answer depends on both a) whether you mean a dominant triad, a dominant seventh, or both; and b) the style of the music in question.

If you mean a dominant triad only, then you're correct: by calling it a dominant, you are implying that this must be V, and therefore you're implying what tonic (I or i) must be.

But as Bennyboy mentions, the dominant seventh chord is so ubiquitous as a particular chord quality—a major triad with minor seventh—that is can be referenced as a chord quality without implying any particular tonic.

To clarify any confusion, plenty of musicians distinguish between a "dominant" and something that is "dominant quality." A dominant must be V, which implies a tonic; but something being dominant quality simply means that it is a dominant-seventh chord, not necessarily built on the fifth scale degree of a particular key.

This is especially clear in other styles of music. In Blues, for instance, you can have a dominant-seventh chord on IV. Obviously it's not functioning as a dominant, but the chord itself is a dominant quality.

Answer 2

The dominant chord is so important as a key-defining chord that it's the only 7th chord referred to just like that: V7.

It also happens that (something like) the minor 7th is the next overtone in the harmonic series after octave, fifth, and major third. In other words, it works not only as a functional tone, but as an extension of harmonic texture.

So yes, the "dominant seventh" is built on the V of a key. But the chord type is so common and versatile as a textural feature, especially in blues or jazz, that when we say "dominant 7th," we are referring to the flavor of the chord, not its diatonic function.