a relative few vs. a relatively few

Engineers in World War I dug through the earth to build serpentine trenches borne from horrifically clear logic.

If enemy soldiers ever breached it, the zigzagging pattern would prevent them from shooting in a straight line down the length of the trench — leaving only a relative few exposed to gunfire or shrapnel.

Is a relatively few possible here? Is there any difference in meaning? If both are possible, which is better and why? Both semantic and syntactic analyses are appreciated.

Solution 1:

Though 'relatively few' is far more modern-sounding than 'a relative few', in this case it doesn't work as there really needs to be a defining nominal in ' ... leaving ____ exposed to ...', or at least a clear antecedent.

' ... leaving only relatively few of the defending soldiers exposed to ...' works and is more modern-sounding (but lengthier and less punchy). Here, 'a relative few' works well, giving something of a WWI period flavour.

Churchill knew that the 'antecedents', the referents, would be globally understood in 'Never in the field of human conflict was so much owed by so many to so few,' when he was of course referring to the heroic efforts of the Royal Air Force crews fighting (and winning) the Battle of Britain.

Using 'a relatively few' in place of 'a relative few' certainly is not unknown (eg 'A relatively few were banded at older ages' [Coloniality in the Cliff Swallow: The Effect of Group Size ... Brown & Brown 1996], but without a headnoun like 'soldiers' it sounds very clumsy to my ears. I'd class it as not ungrammatical, but better avoided (especially in non-period writing). The expression probably jars because of the juxtaposition of adverb (-or-is-it-now?) and [pro-]nominalised quantifier; it probably exists as a reduced form, deleting words without concern for the grammatical mess being left.

Solution 2:

First, you need to observe the distinction between few, which is a negative trigger meaning 'not many'

• Few have ever seen him angry.

and a few, which is affirmative, not negative, and doesn't trigger NPIs like ever

• A few people finally showed up.
• *A few people have ever seen him angry.

They are not the same construction. And they don't have the same syntax, either.

Few is a quantifier, and it modifies a noun phrase. Consequently it can be modified by an adverb like relatively

• Relatively few people have ever seen him angry.

A few, on the other hand, is a determiner, normally used as a noun phrase standing for whatever is being quantified, and as such it is modified by an adjective like relative

• Engineers had to build a relative few trenches. (by comparison)
• Engineers had to build relatively few trenches. (intrinsically negative)

But not the other way around.