In 1984 John Barth published an article titled "The Literature of Replenishment" in Friday Book: Essays and Other Non-Fiction (John Hopkins Press)where modern novel is defined, among other things, as:

the adoption of a tone of epistemological self-mockery aimed at naive pretensions of bourgeois rationality; the opposition of inward consciousness to rational, public, objective discourse; and an inclination to subjective distortion to point up the evanescence of the social world of the nineteenth-century bourgeoisie.

All this points to the modernist novel as a break with all the Victorian literature conventions. It particularly breaks with the cut and dry stylistics of realism by using consciousness as a major denominator. Stylistics, as an approach, is the study of language usage in literature as far as its context and tone; it attempts to explain how and why authors choose the way their characters speak: tone, language, accent, prosody, and other traits of the "personality" of language. Stylistics also analyze the overall use of language in the literary work.

Mrs. Dalloway is a beautiful example of the modern novel precisely because of its use of consciousness as the main character's medium of communication with herself and others. Since consciousness dominates the narrative, Woolf has more license to apply unique traits to distinguish Clarissa and the rest of the characters through the use of their states of mind. The way that Woolf tells her story is not through direct nor indirect characterization. She merely collects all the reflections and thoughts of each of the main characters, as well as the reflections and thoughts of what the other characters feel about them. For example, the reader can "hear" Peter's feelings for Clarissa

'her courage; her social instict'; 'her power of carrying things through'; 'her adventurousness'

we can equally hear Lucezia speak of her husband Septimus.

'[he is] so gentle; so serious; so clever'

Moreover, Woolf even changes the voice of the stream from character to character, making slight breaks even within the disparate narrative style of the novel, causing however no detour from the central vein of the novel.

'That's an E', said Mrs. Bletchley- or a dancer'  and 'It's toffee,' murmured Mr. Bowley'

The end result is a collection of thoughts, emotions, sensations, and points of view that co-exist within a "cloud". This cloud, or condensation of thoughts and emotions, is the vessel that moves the action forward in a non-traditional way

The narrative also features some instances of traditional dialogue, to contrast with the indirect discourse, which is what the stream of consciousness basically is. However, there is yet another pattern of narrative that comes in the form of free, indirect discourse. This consist on NOT revealing directly what the characters are feeling, so that the reader can make inferences and draw conclusions. An example would be:

But Lucrezia herself could not help looking at the motor car and the tree pattern on the blinds. Was it the Queen in there – the Queen going shopping?

Here we see that only Woolf herself would know the answer to Lucrezia's state of mind. Lucrezia is the one thinking, but not even she knows her thoughts exactly. The result is vague and conspicuous use of language to elicit curiosity. Therefore, the complexity in tone and narrative of the novel stems from the state of mind of the characters; this is the  what drives the style of the language.