Before presenting Swinburne’s argument it may be helpful to clarify the difference between a posteriori and a priori reasons for thinking some hypothesis is true.  Suppose that a safe is robbed and our working hypothesis is John stole the money from the safe. During the investigation we may discover two kinds of evidence. First, we may find John’s fingerprints at the crime scene and a sum of money on him matching the sum that was stolen. This will be a posteriori grounds for the truth of the hypothesis; that is, consequences to be expected if the hypothesis is true. Second, we may learn that John has a history of robbing safes and is also in debt. This will be a priori grounds for the truth of the hypothesis; that is, evidence that belongs outside the scope of the hypothesis but nevertheless increases its probable truth. The historical case for the resurrection which I will be presenting later is a posteriori grounds for thinking Jesus was God Incarnate. Like fingerprints on a safe, it is a consequence to be expected if the hypothesis that Jesus rose form the dead is true and not at all to be expected if it is false. The arguments that follow are a priori grounds for thinking that Jesus was God Incarnate. Just as reflection on John’s criminal past and present financial situation may prove him more likely to have committed a crime, so moral reflection on the nature of God and the condition of man may suggest that God is likely to act in certain ways. In what follows, it will be my concern to summarise Swinburne's argument that, given human sin and suffering, a loving God is likely to act in the way Christianity claims he has acted; that is, by becoming incarnate.
The Nature of God and the Condition of Man Swinburne begins his argument with two preliminary points. The first is that God is morally perfect. The second is that human suffering exists in the universe he has created. Such suffering is something which God has good reason to allow but it is also, as we shall see, something to which he is also likely to respond. However, before presenting the argument itself, I will find it helpful to briefly revisit these two points. The moral perfection of God is integral to classical theism. One argument for it unfolds from the observation that voluntary actions always strive towards an apparent good entertained by the agent who performs them. And importantly, this also held for morally bad actions. A thief, for instance, seeks the “good” of an increase in his personal fortune and his action is to be understood as bad insofar as it pursues this small selfish good at the cost of a decrease in the total good—the unhappiness he brings to his victim; the mistrust and unease he inspires; his disruption of social harmony, and so on. However, since all voluntary action is already motivated by the good, and since the good of any action entertained by an agent is dependent on his knowledge and rationality, so increases in knowledge and rationality will refine his judgment of the good and, with that refinement, improve his morality. In a divine mind this principle is developed to its ultimate logical consequence. Being disembodied, God is free from carnality; being omniscient, he is free from irrationality; being omnipotent, he is free from want. His greatest pleasure is therefore found in recognising that he performs virtuous deeds and in pursuing goals which promote universal perfection. Perfect knowledge and power, in short, will produce a perfect awareness of and pursuit of the good. Swinburne suggests that we define the moral perfection of God in this way: God performs only morally best or equally best actions of many kinds and no bad ones. Suffering, meanwhile, is an unpreventable feature of any world in which virtue and moral self-determination are widely attainable for finite agents. This was a point discussed in Chapter 5. Again, briefly: Free will ensures that we have a choice between doing good and doing evil. Humans are so made that when we do good it becomes easier to do good again at the next opportunity and when we do evil it becomes easier to do evil again at the next opportunity.  In this way, we gradually strengthen or weaken desires of different kinds and so form a moral character. Without free will none of this would be possible. And while God is omnipotent his omnipotence needs to be understood in a way that allows for the constraints of logical possibility. And since it is logically impossible for God to create agents with free will and ensure that they do no evil, human suffering is a potential feature of any world in which virtue is attainable. It is because God wants us to freely become good people that he permits temporary moral evil and suffering. But it needs to be noted that it is not free will alone, but free will and moral evil together, that provide an opportunity to manifest most virtues. In other words, only if someone eventually exercises their free will to assault or abuse you can I exercise mine to show you empathy; only if you are robbed can I make personal sacrifices to provide for you. The question arises whether moral evil alone would afford adequate opportunities for everyone to form a virtuous moral character. Swinburne suggests that it would not. A world in which opportunities to obtain virtue are universally available must therefore contain natural evil. Consider again a world without disaster, disease and decrepitude; a world in which the only cause of injury and death is, respectively, assault and murder. It is a mathematical certainty that such a world would provide far, far fewer opportunities for compassion, self-sacrifice, courage, forbearance, and so forth, and highly probable that some of us would have no such opportunities at all. Pleasure and comfort are good and our world, of course, includes both. But a life that offered nothing else would make us complacent, hedonistic, idle, selfish and shallow. The initial conditions of the argument are therefore as follows: Human beings are misusing their free will to do evil. As a result, many individuals and societies are developing a bad moral character. This fact, together with the natural evil necessary to ensure that opportunities to obtain virtue are universally available, causes human suffering that is often widespread and profound. God, meanwhile, is morally perfect. How is he likely to respond? Swinburne argues that God will likely respond by becoming incarnate. Let us now consider the three arguments he gives.
To Fulfil an Obligation to Share in Human Suffering Parents often subject their children to suffering for the sake of some greater good. Mrs Bell, for instance, may put her overweight daughter on a stringent diet. Mr Wild may ask his son to attend a “difficult” neighbourhood school for the sake of good community relations. Under such circumstances, it is good but not obligatory for the parent to show solidarity with their child by taking a share in the suffering that has been imposed. Thus Mrs Bell may decide to join her daughter in eating a green salad for dinner even though Mrs Bell herself is not overweight. And likewise Mr Wild may present himself at the “difficult” neighbourhood school to enrol in the parent-teacher association or offer to coach the soccer team. In both examples the suffering imposed is mild. But Swinburne suggests that when the suffering imposed reaches a certain level of intensity the good of sharing in that suffering for the one who imposes it rises to an obligation. In this connection he offers the following example. Suppose, firstly, that England has been unjustly attacked and the government has conscripted all men between 18 and 30 to defend it; suppose, secondly, that a parent may “veto” the conscription of their son if he is under 21; suppose, thirdly, that older men under 50 may volunteer. Most parents with teenage sons veto the conscription but Swinburne, in view of the gravity of the situation, refuses to do so: He insists that his 19 year old son enlist. Suppose finally that Swinburne is 45 and so himself eligible but under no obligation to serve. “Since I am forcing my son to endure the hardship and danger of military service,” concludes Swinburne, “I have a moral obligation to him to volunteer myself.” And of course in circumstances of this kind the sharing could not be incognito. “The parent needs not merely to share the child’s suffering but to show him that he is doing so.” The relevance of all this to the doctrine of the Incarnation can be spelled out as follows: Given the amount of pain and suffering which God, though for a good purpose, permits us to endure it is very plausible to suppose that he incurs a moral obligation upon himself to share in that suffering; and given that God, being perfectly good, always performs the morally best available action, it is very plausible to suppose that he would discharge that obligation. This could be achieved by means of an incarnation; that is, by becoming human and, “living a life containing much suffering and ending with the great crisis which all humans have to face: the crisis of death.” And one way to ensure that he has shared in the very worst suffering humans must endure is to live a life that ends in a brutal and unjustly imposed execution. A moment ago it was noted that the obligation to share in the suffering one imposes on another can not be discharged in secret. Thus an incarnation would not fulfil its purpose unless the knowledge that it had occurred were made widely available to the future human race. And since the human life of God Incarnate would be of limited duration he must also found an institution to proclaim his message—a point to which we shall return.
To Provide a Means of Making Atonement The second argument begins with three moral concepts: obligation, guilt and atonement. Swinburne divides good actions into two broad types. Obligations are good actions that we owe to others: It is good in this first sense for you to feed your children and tell others the truth. Supererogatory actions are nonobligatory good actions: It is good in this second sense to volunteer at a soup kitchen. We do not wrong others when we fail to perform supererogatory actions but we do wrong others when we fail to meet our obligations—to respect each other's property and personhood, for example, or to keep our promises. For wronging others we are blameworthy and so incur guilt. And in order to remove our guilt we need to “make atonement.” Atonement, Swinburne says, usually has four components: repentance, apology, reparation and penance. If I have stolen your watch I must return it to you or give you something of equivalent value. Such reparation deals with the effects of my wrongdoing but it does not deal with the fact of my wrongdoing—that I sought to harm you. I must also therefore distance myself from my wrongdoing by a sincere apology and repentance. Often this will suffice to remove my guilt but in cases of serious wrongdoing something extra may be required: a small gift or service as a token of my sorrow. Swinburne calls this “making a penance.” The process is completed when the victim agrees to treat me, insofar as he can, as one who has not wronged him: And this is to forgive me. It is an obvious general fact, claims Swinburne, that all humans have wronged God. We have wronged God directly by failing to show reverence and gratitude to him as the holy source of our existence and we have wronged him indirectly by wronging each other. If I hit my wife I abuse the free will and responsibility entrusted to me by God and I also hurt a creature he created—just as I wrong you if I hit your child because I hurt someone upon whom you have lavished your loving care and attention. In addition to incurring guilt through our wrongdoing we inherit a general propensity to wrongdoing. This is partly social (you are more likely to abuse your children if you yourself were abused) and partly genetic: Evidence has emerged that what a person does and has done to him at an early age affects the genes he hands on to his children.  Swinburne suggests that we also inherit something analogous to guilt: We are indebted to our ancestors for our life and for many benefits that come down to us through them; our ancestors, in turn, are indebted to God for their own wrongdoing. We therefore incur an obligation to help atone for their guilt. “Even the English law,” notes Swinburne, “requires that before you can claim what you inherit from your dead parents you must pay their debts.” Thus while the guilt itself is not ours, the obligation to atone for it is, and our failure to meet this obligation can be a further source of guilt. It would seem, then, that human beings have a serious obligation to make atonement and are in a poor position to do so—owing to both the size of the moral debt and the propensity to continued wrongdoing. How might a morally perfect God respond to this? Swinburne suggests that God would likely respond by helping us to make a proper atonement. Earlier I made the obvious point that if I steal your watch I owe you a watch—or something of equal value. The question arises: What is the proper reparation for a wrongdoer to offer God? What has gone wrong, says Swinburne, is that we have failed to live good lives. One proper reparation would therefore be a perfect human life which we can offer to God in repentance. And while that one perfect human life may not morally counterbalance all the wrongdoing of n number of morally bad human lives, it is up to the injured party to determine when a sufficient reparation has been made. And one truly perfect human life would plausibly enable a merciful and morally perfect being to justifiably make that determination. Here the skeptic may still object that a third party cannot make restitution for the offences of another. No one would consider justice done if a judge were to have an innocent man seized off the street and thrown in jail for the crimes of the murderer who himself remained free. Correct. But the problem lies not with the argument but the analogy. Consider a more helpful one. Suppose Mrs Hall hires a man, John, to paint her house. John is paid in advance but procrastinates providing his services and finally spends the money on a ski trip during which he breaks his leg. Ideally, he would either return the money or find someone else to paint the house on his behalf. But if he is incapable of doing either of these things (because, say, he is broke and and doesn't know anyone prepared to paint the house) he finds himself in the position of having an insoluble debt. Plausibly, Mrs Hall could dismiss the whole matter with an airy wave of her hand and hire a new painter. But now suppose the following: That Mrs Hall is a morally conscientious woman who thinks it important that John should take his wrongdoing seriously; that she is very generous; and that sheknows someone who is prepared to paint her house on John's behalf. No one would consider the matter resolved if she were to call this third party and engage him to paint her house without John's knowledge: By every reasonable assessment John would still be in her debt. But she might consider the matter resolved to her satisfaction if John himself were involved in the arrangements—if, for example, he were to express remorse for the situation and then, having been provided with the contact details, were to call the third party in order to explain the problem and ask for his help. In this analogy, needless to say, Mrs Hall represents God, John a human wrongdoer, and Jesus the third party whose assistance we must solicit. As Aquinas noted, confession and contrition must be shown by the sinner himself but, “satisfaction has to do with the exterior act and here one can make use of friends.” Two final points. The first is that there could by chance appear many prophets falsely claiming to be a divine offer of atonement for human wrongdoing. A prophet making the claim truthfully would therefore need the "signature" of God upon his work—an effect that only God can bring about and which can be taken as a mark of endorsement. This would show us that God, the injured party, was willing to accept the reparation. One obvious way God could do this would be to violate the laws of nature—such as by raising the prophet back to life three days after his death. The second final point is that the means of atonement God offers makes no difference to us unless we associate ourselves with it. Just as John, in my analogy, needs to both repent and himself solicit the assistance of the third party in order to discharge his debt, so a wrongdoer needs to ask God to accept the life of Jesus as a reparation for his sins. And this again entails the necessity of a worldwide institution to announce that God has provided a means of atonement and to enjoin us to avail ourselves of it. Swinburne suggests that the Christian claim that Jesus saved us from our sins is to be understood in the above way. By becoming incarnate in Jesus and living a perfect life, God provided a means of atonement. Thus, "God was both the wronged person and also the one who, thinking it so important that we should take our wrongdoing seriously, made available the reparation for us to offer back to him."
To Help Us Live Morally Good Lives Making atonement helps us to deal with past wrongdoings. But God also wants us to live morally good lives in the present; indeed, God wants us, as Swinburne puts it, “to become saints.” This is something most of us obviously fail to do. It is therefore plausible that God would become incarnate for a third reason: To reveal knowledge and found an institution to help us become morally good. Swinburne suggests that this knowledge is of three kinds. Firstly, we need knowledge of what God is like and what he has done in order to properly worship him; for example, that he is a Trinity and shares in our suffering and wishes to provide us with a means of making atonement. Even if we learned these things through a priori arguments, we would still need to know when and as which human God became incarnate so that we can appropriate that atonement to ourselves. And we also need to know something of his future plans for us so that we can make a right response—for example, that there are serious consequences for those who become incorrigibly bad. All this requires a “propositional revelation” from God: a revelation of certain propositions (such as God became incarnate in Jesus Christ) by a trustworthy authority. Secondly, we need moral knowledge about which actions are obligatory and which are supererogatory. Humans, the Bible already affirms, have a natural sense of right and wrong.  But having moral intuition no more guarantees moral living than having a sense of direction guarantees that one will never get lost. It has already been noted that humans have an inherited propensity to wrongdoing. And this can manifest as a tendency to conceal moral truths from ourselves or to interpret them in our preferred way. A parent who sets their child a difficult and risky task (perhaps thinking it is best for the child to learn some things for themselves) may decide to intervene at a critical moment. Seeing that we have failed to live good lives according to what moral awareness is natural to us, it is likewise probable that God would intervene to provide us with moral instruction. Further, because God is our creator and sustainer he has the right to create obligations for us; that is, to issue commands which, if they had not been commanded, would be supererogatory, but, having been commanded, become obligations; i.e., Keep the Sabbath holy. Why would God burden us with these further obligations? Swinburne suggests there are two reasons. The first is to ensure coordination of good actions. Consider, by way of illustration, that is important that drivers travelling in opposite directions agree to keep to opposite sides of the road but unimportant which side they agree to—so long as they do all agree. Likewise, we have a moral obligation to show gratitude to God as our benefactor through worship though doing so on a particular day is only obligatory because God commands it—and God commands a particular day to help ensure that the main obligation is fulfilled. The second reason for creating obligations is help us form the habit of doing what is supererogatorily good. For this same reason a parent may tell a child to do the shopping for a sick neighbour—making a nonobligatory good action obligatory in the hope that the child will develop a habit of doing good beyond what is obligated and so become a morally exemplary person. “If anyone forces you to go one mile,” Jesus instructed, “go with them two miles.” This command may belong to the kind under discussion. This brings us to the third and final way in which an incarnation may help us to live a morally good life. “It would be a lot easier to understand how to live a perfectly good life,” notes Swinburne, “if we have an example of someone doing this.” Thus by becoming incarnate and living a perfect life himself (a life of perfect compassion, pacifism, generosity and love) God provides valuable knowledge and encouragement to his creatures seeking do the same: He not only tells us how to live but shows us—and thereby demonstrates that it can be done and inspires us to emulate him. And yet again for all these purposes to be realised and continue into the future God Incarnate would need to establish a worldwide institution to record, interpret and promulgate his life story and teachings: the Church.
The Christian Doctrine of the Incarnation The Incarnation God is omnipotent, omniscient, omnipresent, eternal. He has these and other properties essentially and this means he cannot cease to have one and remain God any more than a square can cease to have four sides and remain a square. How could God become human and so limited in all of the above respects? “To be human,” explains Swinburne, “is to have a human way of thinking and acting and a human body through which to act.” To become human God would therefore need to acquire a human way of thinking and acting in addition to his divine way of thinking and acting. Freud, the founder of psychoanalysis, showed how a person can have two independent systems of belief; and how, while all the beliefs of such a person are accessible to him, he refuses to admit to his consciousness the beliefs of the one system when he is acting under the other. The Freudian account is derived from cases of self-deception: a pathetic state of which that person needs to be cured. But it helps us to see the possibility of a person willingly keeping a lesser belief system separate from his main belief system and performing different actions under different systems of beliefs—all for some very good reason. In becoming incarnate God allowed himself to develop a second and separate system of human-beliefs acquired through the sensory experience of his human body. The separation of these two belief systems would be a voluntary act—known to his divine mind but not to his human mind. Thus we have a picture of a divine consciousness that includes a human consciousness and a human consciousness that excludes the divine consciousness. It is important to emphasise that God would not have limited his powers by becoming incarnate. He would simply have taken on an additional limited way of operating. And in so doing he would remain divine while acting and feeling much like ourselves. The Virgin Birth The doctrine of the Virgin Birth claims that God caused Mary, the mother of Jesus, to conceive Jesus without that conception involving any sperm from a male human. “It would not have taken a very large miracle,” notes Swinburne, “for God to turn some of the material of Mary’s egg into a second half-set of chromosomes, which, together with the normal half-set derived from Mary, would provide a full set.” But is there any a priori reason for supposing that God would choose to become incarnate in this way? Yes. “It would mean that Jesus came into existence as a human on earth partly by the normal process by which all humans come into existence and partly as a result of a quite abnormal process. It would thus be a historical event symbolizing the doctrine of the Incarnation: that Jesus is partly of human origin and so has a human nature and partly of divine origin and so has a divine nature.” In this way the Virgin Birth would help those who learnt about it later to understand the doctrine of the Incarnation. The Ascension Christian doctrine claims that at the end of his life on earth Jesus, “ascended into the heavens.” Just as, “coming down from the heavens” is clearly to be understood as, “acquired a limited human way of operating,” so “ascended into the heavens,” should be understood as, “abandoned his limited human way of operating.” In the New Testament this event is symbolised by his body rising upwards into the sky until covered by a cloud—something which readers of the Old Testament (in which God manifests as a cloud) would understand as a return to God. Thereafter he remained, “seated at the right hand of the Father”—a phrase which must be understood as, “honourably united to his Father,” since God has no spatial location. An ascension, therefore, has a nonneglibible a priori probability. Like the Virgin Birth, it helps those who learn about it later to better understand the doctrine of the Incarnation.
Conclusion We have seen that it is highly probable that a loving God will become incarnate in response to human sin and suffering: in order to discharge an obligation to share in the suffering which, though for good reason, he allows; to offer wrongdoers a means of making atonement; and to help us live morally good lives by example and instruction. The fulfilment of all three purposes further requires the establishment of a worldwide Church—both to tell us what God Incarnate has done and how we can avail ourselves of it and also to provide guidance and support in living a morally good life. Given the obvious general facts of human sin and suffering, it is highly probable that a loving God will act in the way Christianity claims he has acted. Against the background evidence for bare theism discussed in Part II, Christian doctrine has high a priori probability.
 The phrase a posteriori means posterior to and so, “from what comes after” and the phrase a priori means prior to and so, “from what comes before.”  As Emerson put it, “Sew a thought, reap an action; sew an action, reap a habit; sew a habit, reap a character; sew a character, reap a destiny.”  Swinburne thus understands “Adam and Eve” to symbolise the first humans with free will and moral awareness and “Original Sin” to be the subsequent moment at which conscious wrongdoing began to emerge.  Romans 2:15