what can the actor provide that the dramatist cannot ?
Acting has been described as 'the ability to react to imaginary stimuli', and we should first decide what these 'imaginary stimuli' are. The dramatist may be working from an old story, as Shakespeare did, a thought-out comedy situation, or a cleverly-constructed thriller. Whatever it is, he must first visualize his characters, and not begin writing until they are all as real to him as the members of his family. Unless he does this, he cannot hope to convey a sense of reality to his audience. If he is a good writer, his characters will then emerge as real people, just a little 'larger than life'. But this is far from enough ! It is precisely at this point that his abilities and limitations begin to show. A good play needs a series of dramatic climaxes, with third-act tension and a good denouement.
It also needs far more than words -- many a subtly characterized play fails completely through lack of action, contrast, surprise, stage 'business,' and, in short, general stagecraft. As all this has to be considered, and , broadly speaking, the story comes first rather than the character. There is comparatively little scope for the dramatist to do more than sketch in the 'broad lines,' and these will be done with fairly broad strokes. There will be enough stage directions, but only just enough. In other words, the actor has to supply a great deal that the dramatist cannot, and it is here that the producer, (in the USA., the 'director'), comes in. It is the latter's task to consult carefully with the dramatist, and find out his main intentions, but having done so, the rest is left to the producer. Sometimes, as in the case of the Noel Coward comedies, the main actor is also the author and producer rolled into one, but such individuals are exceptional and outstanding. Normally, the production is in the hands of the producer, and the success of the play will depend on his ability to interpret the dramatist's intentions stagewise, and, if necessary, suggest minor alterations and improvements.
The actor, with the help of the producer, pick up the threads of the production, at the point where the dramatist lays them down. It is up to him to get into the soul of his part, to 'live' in it, as he script-reads and then begins to rehearse. Inevitably, he will get as close as he can to the author's conception of the part, but his own personality is bound to become fused with that of the character he is playing. secondly, the dramatist will have given minimal stage directions, but it is up to the actor, with the producer, to use the arts of gesture, facial movement, stage 'business' (physical occupation on the stage) and stage positioning, to supplement the words he is called on to speak. Thirdly, although the actor is limited to the actual words which he is given by the dramatist, their whole meaning and impact on the audience depend on the actor's own emphasis, use of speed or deliberation, use of the loud or soft voice, use of the whole gamut of emotional overtones or undertones at his command.
In his mind, even in his play, the dramatist may have created a real person, but a real person has a certain appearance, or type of appearance, and the actor inevitably 'stamps' the part or becomes stamped by it. For example, Rupert Davies has in fact become 'Maigret' in the eyes of British television audiences. All these tendencies are even more marked in the film than in the play, where the producer expects to be in complete charge of the finished product, and may even have the original script rewritten ten or more times, and also alter much of the action to achieve the final result he wants. Many a writer for the cinema has ruefully accepted a large fee, and completely washed his hands of a final production which bears little or no resembles to what he originally wrote !