While she is easy to understand in crude functional terms --- like Arabella, she pulls at one extreme of Jude's mixed nature* --- there's a lot more to her personality than that, and it's this "more" that interests me.
(She seems to have interested Hardy, too: Elizabeth Langland, in her 1980 article in Studies in the Novel, cites a letter Hardy wrote in 1895, a year before Jude was first published, in which he says "Curiously enough, I am more interested in the Sue story than in any I have written.")
While the trait most critics (and, indeed, Sue and Jude themselves) single out is Sue's "inconsistency", I noticed a few other odd ones: asexuality, impulsivity, unconventionality, heightened emotional and aesthetic sensitivity, naivete, total frankness and a weird sense of not-quite-thereness with respect to time and place --- her thoughts, feelings and actions don't quite match her age or social position, and the books she's read seem more central to her identity than her family or place of origin. (Now that I lay them all out like this, they sound a bit familiar, except for the inconsistency and emotional lability).
The critical articles I read about Sue (which were Elizabeth Langland's "A Perspective of One's Own," cited above, and Mary Jacobus's 1975 "Sue the Obscure," published in Essays in Criticism) both explained her unusual qualities as a function of the novel's psychological realism, or lack thereof. (Langland argues that Sue's apparent inconsistency comes from her erratic characterization --- she infers from Hardy's own writings about his creative processes that Sue's role evolved somewhat faster than his ability to pin down her personality --- while Jacobus argues the opposite: that Sue's hypocrisy and vacillation make her appear more believably human as she struggles, and fails, to translate her high-minded principles into the tightly constrained sphere of action). Both invoke the distance between most of the narration (in which Jude's is the primary perspective) and Sue's thoughts and feelings. Jacobus observes that, while we get a little of Sue's perspective early in the novel, recurring infrequently up until the deaths of the children, after that point we hear nothing from her point of view. Her mental breakdown renders her mind inaccessible, both to Jude and to us.
Actually, for a character who's supposedly such a riddle to critics, Sue looked awfully familiar to me (and it wasn't just because I'd fairly recently read Jane Eyre, whose heroine is similarly bookish and unworldly). I found several passages in which I was able to identify with her completely, which you might guess rarely happens. Her emotional transports and childlike glee map fairly easily onto the immanence I experience as part of my sensory hypersensitivity, and her identification with the Venus Urania really speaks to me as a (mostly) asexual who sets a lot of store by intellectual romance. Also, as someone whose most significant (and longest-lasting) "perseveration" was Greek mythology, I was quite pleased when she smuggled the statues of Aphrodite and Apollo into her room at Miss Fontover's house.
Here, Sue relates to Jude how she came by her education:
"You called me a creature of civilization, or something, didn't you?" she said, breaking a silence. "It was very odd you should have done that."The above passage, with its reference to "unwholesome" parts in books that cease to interest Sue once she's able to decipher their innuendoes ("Oh, that's all they were talking about? Yuck!"), hints at Sue's asexuality.
"Well, because it is provokingly wrong. I am a sort of negation of it."
"You are very philosophical. 'A negation' is profound talking."
"Is it? Do I strike you as being learned?" she asked, with a touch of raillery.
"No --- not learned. Only you don't talk quite like a girl --- well, a girl who has had no advantages."
"I have had advantages. I don't know Latin and Greek, though I know the grammars of those tongues. But I know most of the Greek and Latin classics through translations, and other books too. I have read Lemprière, Catullus**, Martial, Juvenal, Lucian, Beaumont and Fletcher, Boccaccio, Scarron, De Brantôme, Sterne, De Foe, Smollett, Fielding, Shakespeare, the Bible, and other such; and found that all interest in the unwholesome parts of those books ended with its mystery."
"You have read more than I," he said with a sigh. "How came you to read some of those queerer ones?"
"Well," she said thoughtfully, "it was by accident. My life has been entirely shaped by what people call a peculiarity in me. I have no fear of men, as such, nor of their books. I have mixed with them --- one or two of them particularly --- almost as one of their own sex. ..." (emphases mine)
Here are a few more such passages:
"[Other people's] views on the relations of man and woman are limited, as is proved by their expelling me from the school. Their philosophy only recognized relations based on animal desire. The wide field of strong attachment where desire plays, at least, only a secondary part, is ignored by them --- the part of --- who is it? --- Venus Urania."and
Then the slim little wife of a husband whose person was disagreeable to her, the ethereal, fine-nerved, sensitive girl, quite unfitted by temperament or instinct to fulfil the conditions of the matrimonial relation with Phillotson, possibly with scarce any man, walked fitfully along, and panted, and brought weariness into her eyes by gazing and worrying hopelessly.I also have an alternate reading for her inconsistency and vacillation: she doesn't self-censor. Rather than sequestering her decision-making process away in the privacy of her own mind she thinks aloud, particularly to those she deems her friends and intellectual soulmates, like Jude and Phillotson. So she speaks, and acts, on whatever impulse enters her head, and often as not she will decide later (sometimes immediately after the fact) that she did the wrong thing and must go and make amends immediately.
(I share the lack of self-censorship with her, but do not share the flightiness and impulsivity. I am a very slow thinker, and do not ping-pong between options as Sue seems to do so much as shape the choice I will make out of the amorphous goo that in my mind's eye represents what might be).
Sue's disavowal of her gender (which comes up fairly often, as in the first passage I quote where she claims to mix with men as one of them), and of gender itself, is also familiar to me, and comes up with some frequency in the writings of autistic women. For her, androgyny and asexuality are both linked to her intellectual nature --- not because, as D. H. Lawrence saw it, she is an unwomanly woman, a bundle of essentially masculine urges to philosophize, to name things, to interpret, to systematize; all at the expense of the passive, maternal Feminine --- but possibly because she correctly perceives the dangers independent-minded women of her time brave when they choose to be sexual. For most, sex and romance lead to marriage, which in her time still means becoming someone's property. Your movement and social interactions become greatly restricted, lest your morals be questioned. Even if Sue were not, as the novel makes it clear she is, a natural asexual, she would have some very compelling reasons to try to stay celibate anyway.
It seems like the more I read, especially these old-but-not-too-old books, the more I run into these startlingly autistic-like characters. I think the Victorian novel in particular seems to produce a lot of them, if only out of a need for highly idiosyncratic characters to pit against a stifling social order.
*I did find it problematic that, while Jude gets to be fully, messily human, containing both fleshly appetites and spiritual aspirations, each of the female characters is given just one of these aspects of humanity. Madonna/whore dichotomy, anyone?
**A friend of mine who reads Latin tells me Catullus is pretty risqué. I wonder, given the history of later, especially 19th-century, translators of older texts altering, or leaving out entirely, those parts of the originals they found objectionable, whether Sue would have been able to get a reasonably faithful translation of Catullus at all.