Modernism was an experimental form with a focus on language and interiority. It reacted to and rejected the Victorian and Edwardian emphases on describing external characteristics of a place or character in an objective manner. It also often rejected the omniscient narrator. Instead, it put an emphasis on the subjective interiority of individual characters' experiences and the limited way they perceived the world.
As mentioned in the answer above, To the Lighthouse is a highly subjective stream-of-consciousness novel told primarily through the minds of its characters. I would add that it also experimented radically with time. Most of the novel—hundreds of pages—covers just one day, while in Part II, ten years pass in a few pages. Part III comprises just a morning. This reflected Woolf's sense that time was difficult, if not impossible, to capture in words. As she put it in the novel:
The urgency of the moment always missed its mark. Words fluttered sideways and struck the objects...
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