The distinction suggested by Kant his Critique of Practical Reason is between perfect obligations and imperfect obligations.
The introduction of imperfect obligations extends the reach of human rights to this universal level by involving "the demand that serious consideration be given by anyone in a position to provide reasonable help to the person whose human right is threatened.
As a means of answering this critique, Sen returns to the concept he has already developed about the different kinds of obligations a right establishes upon human agents, in particular, both perfect and imperfect obligations.
By surfacing Kant's distinction between perfect and imperfect obligations in the context of what are thought to be important and influenceable freedoms, Sen has provided the moral argument against those who would say "it's not my problem.
Yet it seems clear that imperfect obligations
can be established as preconditions for entry into the rights-based realm we commonly associate with citizenship.
In contrast, Mill thought imperfect obligations
could not be enforced by the state; they were obligations that we should perform, but we were free to choose the time and circumstances of our performance.
To begin with rights and suppose that obligations emerge as mere correlatives of these is to rule out this possibility from the beginning, The book provides logically independent distinctions between perfect and imperfect obligations
(those that do and those that do not give rise to correlative rights) and between universal and special obligations (those had by all persons and those arising from special relations).
61)) The obligation in question is then an imperfect obligation, using this term in contrast to a perfect obligation to mark the distinction between obligations with counterpart rights (namely, perfect obligations) and obligations without counterpart rights (namely, imperfect obligations).
Campbell, "Perfect and Imperfect Obligations," The Modern Schoolman 52 (1975): 285-94.
So to answer my question: While making an adoption plan is justifiable when, during a pregnancy, parents realize that they cannot provide for the child as they are obliged to do, to seek to conceive a child with the idea of giving him or her up is wrong since it flouts the special imperfect obligation that a parent has toward his or her child to seek to make his or her life good in ways that only a parent can.
In other words, while it appears that the surrogate does not violate any perfect obligations toward the child, the surrogate may violate an imperfect obligation toward the child to love him or her in ways that only a parent can.