There's a section in one of her essays that deals with the reality that lies below the surface. In it she says there's no single reality that we all acknowledge to exist. In fact truth is frequently more fanciful than prosaic: "We know indeed that this reality is a chameleon quality, the fantastic becoming as we grow used to it often the closest to the truth, the sober the furthest from it, and nothing proving a writer's greatness more than his capacity to consolidate his scene by the use of what, until he touched them, seemed wisps of cloud and threads of gossamer."
This treatment of truth, with its conclusion that a writer achieves greatness when able to direct the reader's perception below the surface without sacrificing verisimilitude, leads me to see what what it was that Woolf was attempting to achieve -- did achieve -- in her characterizations of Septimus and Clarissa.
She gives both these characters a intense perception of their surroundings. For Septimus, the perception is not hallucinatory, but he sees it as an aberration, a heightened sense of reality that normal people do not possess. For Woolf, this is one aspect of his insanity. Clarissa also has an intense awareness of things, but she is the author's "sane" character.
The difference between the two seems to lie in the degree of each character's self-control. Septimus has no control. He is emotionally drained, prey to his perceptions. Woolf described an episode of this nature from her own life. It appears in her diary entry for a day in the period in which she was writing Mrs. D. The entry shows Woolf herself to have an uncontrolled Septimus-like stepping outside normal reality with heightened awareness of what's around her. I've put the entry at bottom of this post.
Clarissa does not have attacks of this nature. She perceives things brilliantly but is not a victim of the "the old devil" who "has once more got his spine through the waves" (Woolf's words in the diary entry).
As I see it, Clarissa has found the method of controlled perception as does Woolf's imaginary playwright in the following passage. That is, she can let her fancy range free and also keep herself grounded in that reality which, to the Bennett's of the world, is genuine. She can perceive both poetic and prosaic truth. She can, as the passage has it, both wander in the land of the unicorn and also keep one toe touching Liverpool.
This passage is from an essay on which she was working while she was writing Mrs. D: NOTES ON AN ELIZABETHAN PLAY
At the outset in reading an Elizabethan play we are overcome by the extraordinary discrepancy between the Elizabethan view of reality and our own. The reality to which we have grown accustomed, is, speaking roughly, based upon the life and death of some knight called Smith, who succeeded his father in the family business of pitwood importers, timber merchants and coal exporters, was well known in political, temperance, and church circles, did much for the poor of Liverpool, and died last Wednesday of pneumonia while on a visit to his son at Muswell Hill. That is the world we know. That is the reality which our poets and novelists have to expound and illuminate. Then we open the first Elizabethan play that comes to hand and read howI once did see In my young travels through Armenia An angry unicorn in his full career Charge with too swift a foot a jeweller That watch'd him for the treasure of his brow And ere he could get shelter of a tree Nail him with his rich antlers to the earth.
Where is Smith, we ask, where is Liverpool'? And the groves of Elizabethan drama echo "Where '?" Exquisite is the delight, sublime the relief of being set free to wander in the land of the unicorn and the jeweller among dukes and grandees, Gonzaloes and Bellimperias, who spend their lives in murder and intrigue, dress up as men if they are women, as women if they are men, see ghosts, run mad, and die in the greatest profusion on the slightest provocation, uttering as the fall imprecations of superb vigour or elegies of the wildest despair. . . .
Is it not that literature, if it is to keep us on the alert through five acts or thirty-two chapters must somehow be based on Smith, have one toe touching Liverpool, take off into whatever heights it pleases from reality? We are not so purblind as to suppose that a man because his name is Smith and he lives at Liverpool is therefore "real". We know indeed that this reality is a chameleon quality, the fantastic becoming as we grow used to it often the closest to the truth, the sober the furthest from it, and nothing proving a writer's greatness more than his capacity to consolidate his scene by the use of what, until he touched them, seemed wisps of cloud and threads of gossamer. Our contention merely is that there is a station, somewhere in mid-air, whence Smith and Liverpool can be seen to the best advantage; that the great artist is the man who knows where to place himself above the shifting scenery; that while he never loses sight of Liverpool he never sees it in the wrong perspective.
-- From: The Common Reader, First Series, by Virginia Woolf (1925), pp 74-75.
From the Diary:
Monday, 15 October, 1923 -- -- Hogarth
This last entry seems long ago. And I meant to record for psychological purposes that strange night when I went to meet Leonard & did not meet him. What an intensity of feeling was pressed into those hours! It was a wet windy night; & as I walked back across the field I said Now I am meeting it; now the old devil has once more got his spine through the waves. (but I cannot re-capture really). And such was the strength of my feeling that I became physically rigid. Reality; so I thought, was unveiled. And there was something noble in feeling like this; tragic, not at all petty. Then cold white lights went over the fields; & went out; & I stood under the great trees at Hord waiting for the lights of the bus.
And that went by; & I felt lonelier. There was a man with a barrow walking into Lewes, who looked at me. But I could toy with, at least control all this, until suddenly, after the last likely train had come in I felt it was intolerable to sit about, & must do the final thing, which was to go to London. Off I rode, without much time, against such a wind; & again I had a satisfaction in being matched with powerful things, like wind & dark. I battled, had to walk; got on; drove ahead; dropped the torch; picked it up, & so on again without any lights. Saw men & women walking together; thought, you're safe & happy I'm an outcast; took my ticket; had 3 minutes to spare, & then, turning the corner of the station stairs, saw Leonard, coming along, bending rather, like a person walking very quick, in his mackintosh. He was rather cold & angry (as, perhaps was natural). And then, not to show my feelings, I went outside & did something to my bicycle. Also, I went back to the ticket office, & said to the humane man there, "Its all right. My husband caught the last train. Give me back my fare" which he did. And I got the money more to set myself right with Leonard than because I wanted it. All the way back we talked about a row (about reviewers) at the office. ( & all the time I was feeling My God, thats over. I'm out of that. Its over. Really, it was a physical feeling, of lightness & relief & safety. & 'j there was too something terrible behind it -- the fact of this pain, suppose; which continued for several days -- I think I should feel it again if I went over that road at night; & it became connected with the death of the miners, & with Aubrey Herbert's death next day.* But I have not got it all in, by any means. . . .
* On 25 September 1923 the No. 23 Redding Pit near Falkirk was flooded and 41 men lost their lives. Lt.-Col. Aubrey Herbert MP (b. 1880), died on 26 September 1923; he was a half-brother of Lady Margaret Duckworth.