"[…] she ought to make her way with 'en, if she plays her trump card aright. And if he don't marry her afore he will after." (7.37)
Mrs. Durbeyfield can tell that Alec is totally lusting after Tess, but she sends her off to work for the D'Urbervilles anyway, assuming that if Alec doesn't marry her "before" (sleeping with her), he will "after."
Phase II: "Maiden No More," Chapter Twelve
"And yet th'st not got him to marry 'ee!" reiterated her mother. "Any woman would have done it but you!" (12.76)
Tess comes home having been raped by Alec, but without having married him. This totally overturns Mrs. Durbeyfield's views of sex and marriage. Yes, marriage is generally supposed to happen first, but on the occasions when sex happens first, marriage is sure to follow – or so Mrs. Durbeyfield had persuaded herself.
Phase IV: "The Consequence," Chapter Thirty-One
There was hardly a touch of earth in her love for Clare. To her sublime trustfulness he was all that goodness could be – knew all that a guide, philosopher, and friend should know. She thought every line in the contour of his person the perfection of masculine beauty, his soul the soul of a saint, his intellect that of a seer. (31.6)
Tess looks up to Angel as some kind of supreme being. Not surprising, given his name (see "Character Analysis" section for Angel, and the "Character Clues" section for more on that). But the tragedy of the second half of the novel really stems from the fact that both Tess and Angel love the other as a supreme being – and both are disappointed when the find that the other is only human.
Phase IV: "The Consequence," Chapter Thirty-Two
"[…] since you will probably have to leave at Christmas, it is in every way desirable and convenient that I should carry you off then as my property." (32.18)
It's surprising to realize that even a relatively good man like Angel Clare would buy into the idea that a wife is her husband's property.
Phase IV: "The Consequence," Chapter Thirty-Three
By the time they reached home she was contrite and spiritless. She was Mrs. Angel Clare, indeed, but had she any moral right to the name? Was she not more truly Mrs. Alexander D'Urberville? Had intensity of love any power to justify what might possibly be considered in upright souls as culpable reticence? (33.53)
Just after her marriage to Angel, Tess muses on the difference between natural law and social laws. Is there a difference between the two? If "marriage" is just a physical union between two people resulting in procreation then, sure, she married Alec D'Urberville. Or, to be fair, he married her. Without permission. Or is love a social union? If so, then she's only married to Angel.
Phase V: "The Woman Pays," Chapter Thirty-Six
"How can we live together while that man lives?" (36.82)
In other editions, Angel adds that Alec is Tess's husband in nature, if not legally. So again, there's a distinction between natural law and social law.
Such is the vulpine slyness of Dame Nature, that, till now, Tess had been hoodwinked by her love for Clare into forgetting it might result in vitalizations that would inflict upon others what she had bewailed as a misfortune to herself. (36.86)
Tess realizes that if she manages to persuade Clare to stay with her by getting him to consummate their marriage (i.e., to have sex with her), she might get pregnant. But to call those potential children "vitalizations" sounds awfully clinical and distant. She thinks of their possible children as future sufferers at the hands of an unjust world, and simply as "vitalizations" – living things. And living things, as we know from reading Hardy, suffer.
Phase V: "The Woman Pays," Chapter Forty-One
She was ashamed of herself for her gloom of the night, based on nothing more tangible than a sense of condemnation under an arbitrary law of society which had no foundation in Nature. (41.33)
Tess sees the dying birds in the early morning, and puts them out of their misery out of pity. She realizes that she's not actually the most miserable living creature in the world – she hasn't been shot by hunters and left for dead. She's only been "condemn[ed]" by "an arbitrary law of society." So again, there's a distinction being made between Nature's laws, and the laws of society. The only law Tess "broke" (sex before marriage) is a social law, and one that has "no foundation in Nature."
Phase V: "The Woman Pays," Chapter Forty-Two
"I'll always be ugly now, because Angel is not here, and I have nobody to take care of me. My husband that is gone away, and never will love me any more; but I love him just the same, and hate all other men, and like to make 'em think scornful o' me!" (42.5)
Angel might have left her, but Tess remains fiercely loyal to him to the point of making herself ugly so that other men won't admire her good looks. Her idea of marriage seems to be that no other men should even look at her if she can help it. But really, her decision to make herself ugly is a practical one – she was getting harassed on the road.
Phase VI: "The Convert," Chapter Forty-Seven
"Remember, I was your master once! I will be your master again. If you are any man's wife you are mine!" (47.39)
Alec is angry after Tess smacks him with a heavy work glove, and he actually says what he thinks: that he has some kind of natural right to Tess, just because he's the first man to have had sex with her. In his mind, this makes him her "natural" husband.