One of the conundrums of Christian sexual ethics is that the Bible does not directly and explicitly forbid premarital sex, as it does, for example, adultery and homosexual activity. In my experience, most pastors argue that the Bible conveys a general sense that sexual activity is moral within marriage even though it does not openly condemn it prior to marriage, or argue that people and society are better off if premarital chastity is normative.
Joe Carter has laid out an argument that people have a moral obligation to refrain from pre-marital sex to honor their future spouses:
Of the specific obligations that spouses owe, some are shared by other people (e.g., parents) throughout a person's life while others are unique to the matrimonial bond. For example, a husband has the obligations to financially support and to remain sexually faithful to his wife. The financial obligation is one that is first met by the parents, and perhaps later by the woman herself. The future husband is not expected to provide for her materially before they have even met. The fidelity obligation, however, is a unique duty that is not shared by any other person. It is specific to the marital relationship and is therefore binding even before the two "soul mates" have found each other.
Consider this thought experiment. Imagine a man is to be married on February 14th and has sexual relations with a woman who is not his fiance on:
(a) The night before his wedding. (b) The day of his wedding. (c) The day after his wedding.
The action in each instance is the same but the term we'd use to describe the man would depend on when the event occurred: (a) would make the man a cheating cad, (c) and adulterer, and (b) either a cheating cad or an adulterer, depending on the time of day. Regardless of what we choose to call it, the consequence of the action is the same -- the man has been unfaithful to the woman. Notice that though the "temporal perspective" changes the semantics, it doesn't change the morality of the action.
The argument is limited. Here is my own thought experiment: Let us say that tonight, as a married man, I went out on a date with a woman other than my wife. We had a romantic dinner and a walk by the lake in moonlight. Would that be adultery? Yes. I would be violating the emotional boundaries of my marriage.
Now, let us say that this event did not take place tonight, but eight years ago, long before I had met Katherine. Would that be adultery? No, at least under any definition that I can understand. I was under no obligation to refrain from dating this hypothetical woman to honor an even more hypothetical future bride. In fact, if I viewed dating as adultery against a hypothetical bride, then I would never have gone on a first date with Katherine at all.
So Carter is incorrect: the temporal perspective does change the morality of an action. His example only seems correct because he has limited the time frame to immediately preceding and after a planned wedding.
Which is not to say that premarital sex is moral or wise. It is not. But Carter has failed to provide a complete argument to that effect.
UPDATE: In his comments, Carter responds to my argument that if I went on a non-sexual date with a woman right now, even though I am married, that it would constitute adultery:
No, it would not be adultery (Voluntary sexual intercourse between a married person and a partner other than the lawful spouse). Having emotional attachments are not forbidden nor would a person be (necessarily) morally obligated to refrain from forming such bonds.
I disagree. Marriage is more than a commitment to sexual monogamy; it is also a commitment to sharing certain feelings (like romantic love) only with one's spouse.