Adjective
Let us first consider the use of the most-combillation with the indefinite article.This combination is a common means of expressing elative evaluations of substance properties. The function of the elative most-construction in distinction to the function of the superlative most-'construction will be seen from the following examples:
The speaker launched a most significant personal attack on the Prime
Minister. The most significant of the arguments in a dispute is not necessarily the most spectacular one.
While the phrase "a most significant (personal) attack" in the first of the two examples gives the idea of rather a high degree of the quality expressed irrespective of any directly introduced or implied comparison with other attacks on the Prime Minister, the phrase "the most significant of the arguments" expresses exactly the superlative degree of the quality in relation to the immediately introduced comparison with all the rest of the arguments in a dispute; the same holds true of the phrase "the most spectacular one". It is this exclusion of the outwardly superlative adjective from a comparison that makes it into a simple elative, with its most-constituent turned from the superlative auxiliary into a kind of a lexical intensifier.
The definite article with the elative most-construction is also possible, if leaving the elative function less distinctly recognizable (in oral speech the elative most is commonly left unstressed, the absence of stress serving as a negative mark of the elative). Cf.: I found myself in the most awkward situation, for I couldn't give a satisfactory answer to any question asked by the visitors.
Now, the synthetical superlative degree, as is known, can be used in the elative function as well, the distinguishing feature of the latter being its exclusion from a comparison.
Cf.:
Unfortunately, our cooperation with Danny proved the worst experience for both of us. No doubt Mr. Snider will show you his collection of minerals with the greatest pleasure.
And this fact gives us a clue for understanding the expressive nature of the elative superlative as such — the nature that provides it with a permanent grammatico-stylistic status in the language. Indeed, the expressive peculiarity of the form consists exactly in the immediate combination of the two features which outwardly contradict each other: the categorial form of the superlative on the one hand, and the absence of a comparison on the other.
That the categorial form of the superlative (i.e. the superlative with its general functional specification) is essential also for the expression of the elative semantics can, however paradoxical it might appear, be very well illustrated by the elative use of the comparative degree. Indeed, the comparative combination featuring the dative comparative degree is constructed in such a way as to place it in the functional position of unrestricted superiority, i.e. in the position specifically characteristic of the superlative. E.g.:
Nothing gives me greater pleasure than to greet you as our guest of honour.
There is nothing more refreshing than a good swim.
The parallelism of functions between the two forms of comparison (the comparative degree and the superlative degree) in such and like examples is unquestionable.
As we see, the elative superlative, though it is not the regular superlative in the grammatical sense, is still a kind of a specific, grammatically featured construction. This grammatical specification distinguishes it from common elative constructions which may be generally defined as syntactic combinations of an intensely high estimation. E.g.: an extremely important amendment; a matter of exceeding urgency; quite an unparalleled beauty; etc.
Thus, from a grammatical point of view, the elative superlative, though semantically it is "elevated", is nothing else but a degraded superlative, and its distinct featuring mark with the analytical superlative degree is the indefinite article: the two forms of the superlative of different functional purposes receive the two different marks (if not quite rigorously separated in actual uses) by the article determination treatment.
It follows from the above that the possibility of the most-combination to be used with the indefinite article cannot in any way be demonstrative of its non-grammatical character, since the functions of the two superlative combinations in question, the elative superlative and the genuine superlative, are different.
Moreover, the use of the indefinite article with the synthetical superlative in the degraded, dative function is not altogether impossible, though somehow such a possibility is bluntly denied by certain grammatical manuals. Cf.: He made a last lame effort to delay the experiment; but Basil was impervious to suggestion.But there is one more possibility to formally differentiate the direct and dative functions of the synthetical superlative, namely, by using the zero article with the superlative. This latter possibility is noted in some grammar books (Ganshina, Vasilevskaya, 85). Cf.: Suddenly I was seized with a sensation of deepest regret.
However, the general tendency of expressing the superlative dative meaning is by using the analytical form. Incidentally, in the Russian language the tendency of usage is reverse: it is the synthetical form of the Russian superlative that is preferred in rendering the dative function.