Another of the friars and I were talking about limbo, the idea that there is some kind of eschatological destiny that corresponds to perfect natural happiness for the human person. This is opposed, of course, to the idea of heaven, which is perfect supernatural happiness.
At certain points in the history of Christian theological reflection, limbo served as a solution to two theological problems. First, where did the patriarchs, prophets, and righteous people of God of the old covenants await the resurrection they would receive in Christ? This is the so-called limbo of the fathers. Second, what becomes of infants who do not receive baptism through no fault of their own? Certainly God would not deny them a happy destiny! So perhaps there is a state on the "border" or limbus of hell, that corresponds to natural fulfillment, short of the supernatural fulfillment of heaven. This seems to have been the view of St. Thomas, though we have to say that Thomas was not always real good on eschatology; after all he didn't really want to accept the Immaculate Conception. And oh yes, the Immaculate Conception is a doctrine about eschatology and ultimate destiny.
Now folks will point out, quite correctly, that we don't talk about limbo anymore. Indeed, the Catechism of the Catholic Church, when it faces the question of unbaptized infants doesn't mention it all but holds out a well-founded and confident hope for their highest salvation.
But this doesn't mean that there is no such thing as limbo; doctrine is accurate to Truth, but it does not exhaust Truth. This is especially true when we are talking about something as difficult as the Last Things. Limbo remains a theological possibility. There are other things like this, theological possibilities that we don't talk about or teach because they are too unsure. For another example, I think it's entirely theologically possible that two or three presbyters (i.e. priests who aren't bishops) could ordain a layman a deacon, or ordain a deacon a priest. But we can't be so sure about this, so we don't put the validity of sacramental ministry in danger by doing such a thing.
For me, I don't have a problem accepting the idea of limbo. To me it sounds pretty good: a state of eternal, perfect happiness on the natural level for those who were denied baptism of water, desire, or blood through no fault of their own. It's not the perfect supernatural happiness of heaven which we begin to live in baptism, but it doesn't sound so bad.