This following is an excerpt from chapter 2 of my One Body book.
One sense of “unconditional” is negative: there are no conditions on account of which one is loving the beloved. This negative sense, however, denies the truism that if someone loves you unconditionally, you can count on his or her love. A love that comes about for no reason at all might, as already noted, equally well disappear for no reason.
Let us, then, hold on to the truism. An unconditional love is one you can count on, no matter what. On the face of it, this makes unconditional love something humanly unattainable. For in our earthly lives, brainwashing and sin are always possible: the continuation of love is never completely certain. There is no present state of earthly love that guarantees a future continuation. It is plainly a myth, though a not uncommon one, that the way two people love each other at the beginning of their relationship determines the future course of the relationship.
The unattainability objection to the possibility of unconditional love understands an unconditional love as one that is certain to last. This would mean that if I said that I love my children unconditionally, I would be presumptuously asserting that my future love will last forever. But we need to distinguish two senses of the claim that one “can count on” the loving continuing. In one sense, something can be counted on provided that you have epistemic certainty of its truth. But there is another sense: we can read “can count on” as “have the right to count on,” in the way that you have the right to count on people to keep their promises to you. But you only have the right, in the relevant sense, to count on my doing something if I owe it to you to do it. Having the right to count on someone to do something is correlated with an obligation on the part of that person. Thus, unconditional love is a present love that the lover is obligated to persevere in no matter what (even if the beloved should no longer desire that perseverance—this is important in the case of children, who have the right to count on their parents loving them even at times when the children might say that they don’t care about the parents’ love).
The obligation to persevere, however, is not enough to make a love unconditional. All parents have the obligation to love their children no matter what, but not all love their children unconditionally. Thus, to say that a love is unconditional if and only if that the obligation to continue loving is certain to be kept would be to make unconditional love unattainable in our earthly lives. But to say that a love is unconditional simply providing that there is an obligation to continue loving, whether or not the lover accepts the obligation, would also not be enough. We need something in between. The notion of commitment gives us what we need. An unconditional commitment to a moral obligation is an unreserved acceptance of the obligation. Such an acceptance does not make certain the fulfillment of the obligation—we do sometimes wrongfully go back on our commitments, after all—but it does set one on the path to fulfillment, and gives others reason to think we will fulfill the commitment. It is worth noting here that probably only an obligation can be accepted unconditionally, unreservedly, because we are unable to predict the future with great certainty, and anything other than a moral obligation may be something that one day we might have a reason to go against.
Unconditional love, thus, includes an obligation and an unreserved acceptance of the obligation.