In a letter to Vita Sackville-West (16 March 1926), Woolf wrote:

As for the mot juste, you are quite wrong. Style is a very simple matter; it is all rhythm. Once you get that, you can’t use the wrong words. But on the other hand here am I sitting after half the morning, crammed with ideas, and visions, and so on, and can’t dislodge them, for lack of the right rhythm. Now this is very profound, what rhythm is, and goes far deeper than words. A sight, an emotion, creates this wave in the mind, long before it makes words to fit it; and in writing (such is my present belief ) one has to recapture this, and set this working (which has nothing apparently to do with words) and then, as it breaks and tumbles in the mind, it makes words to fit it: But no doubt I shall think differently next year.

Woolf ’s assertion that rhythm is style and ‘a very simple matter’ is thus immediately countered by a claim for its complexity. If her ideas are placed in the context of her correspondence with Sackville-West, it becomes clear that she was responding to the latter’s view that ‘style and surface-texture’ should receive greater attention from critics and that the perfection of Woolf ’s ‘style’ (rivalled, Sackville-West suggested, only by that of Max Beerbohm) came, enviably, at no cost ‘of thought or trouble’. Woolf ’s response was that while ‘style’ might indeed be a ‘simple matter’ the question of ‘rhythm’ (on which the choice of words was dependent) was in fact ‘profound’, going ‘far deeper than words’ and, by implication, than ‘surface-texture’ (Sackville-West’s phrase), and entailing much creative effort in the ‘recapture’ of the rhythmic movement and the ‘exact shapes’ of consciousness. The imaginative process, she indicates, was a plunge (the word she uses at the opening of Mrs Dalloway), while her watery-depth metaphors were a foretaste of The Waves, written, as Woolf observed to the musician and composer Ethel Smyth, ‘to a rhythm and not to a plot’: ‘And thus though the rhythmical is more natural to me than the narrative, it is completely opposed to the tradition of fiction and I am casting about all the time for some rope to throw to the reader.’ The rhythm of the waves, taking up the earlier image of ‘the wave in the mind’, sounds throughout the interludes that punctuate The Waves, as Woolf finds images to represent the passage of time, and of light, from dawn to darkness and, in the final pages of the novel, to dawn again: ‘Yes, this is the eternal renewal, the incessant rise and fall and fall and rise again.’ The motif became central to the construction of the novel’s unity and Woolf ’s desire to represent simultaneity rather than sequence (as in her intention for the final section of To the Lighthouse to represent two things happening at the same time): ‘The Waves is I think resolving itself … into a series of dramatic soliloquies. The thing is to keep them running homogeneously in & out, in the rhythm of the waves.’

[In a footnote:]  In a further letter to Smyth, Woolf wrote of the disturbances of listening to Wagner on the radio: ‘His rhythm destroys my rhythm; yes, thats [sic] a true observation. All writing is nothing but putting words on the backs of rhythm. If they fall off the rhythm one’s done … Thank God, Wagner has  stopped murmuring among the forest leaves, and I’m my own mistress again’; ibid., vol. 4, 303–5 (7 April 1931).

Laura Marcus, Rhythmical Subjects: The Measures of the Modern