Many philosophers throughout the course of religious history have drawn upon proofs and evidences to suggest that the existence evil and suffering undermines theistic belief. For instance, William L. Rowe in his argument in An Exchange on the Problem of Evil  first asks, “Do the evils that occur in our world significantly lower the likelihood of God’s existence?”  Philosophers of course have taken their respective position on this question. Rowe for instance, believes that given the existence of evil this would constitute a very unlikely chance that God exists:
[T]he evils that occur in our world make belief in atheism more reasonable than belief in theism. If we put aside grounds for belief in the existence of God, the likelihood that God exists cannot be reasonably be assigned any probability beyond .5 – where 1 represents God’s existence as certain, and 0 represents certainty that God does not exist. 
However, stronger theses can be seen from J.H. McCloskey where he argues that “[e]vil is a problem for the theist in that a contradiction is involved in the fact of evil, on the one hand, and the belief in the omnipotence and perfection of God on the other” . J.L. Mackie moreover has argued elsewhere the logical problem of evil in its full force , suggesting that “God is omnipotent; God is wholly good; and yet evil exists. There seems to be some contradiction between these three propositions, so if any two of them were true the third would be false. But at the same time all three are essential parts of most theological positions: the theologian, it seems, at once must adhere and cannot consistently adhere to all three” .
Mackie further goes on to argue that
[i]f God has made men such that in their free choices they sometimes prefer what is good and sometimes what is evil, why could he not have made men such that they always freely choose the good? If there is no logical impossibility in a man’s freely choosing the good on one, or on several occasions, there cannot be a logical impossibility in his freely choosing the good on every occasion. God was not, then, faced with a choice between making innocent automata and making beings who, in acting freely, would sometimes go wrong; there was open to him the obviously better possibility of making beings who would act freely but always go right. Clearly, his failure to avail himself of this possibility is inconsistent with his being both omnipotent and wholly good. 
Thus, the structure of Mackie’s argument can be as follows :
- (1) God is omnipotent and omniscient and wholly good.
- (2) If God is omnipotent, He can create or bring about any logical possible state of affairs.
- (3) God can create any logically possible state of affairs – (1), (2)
- (4) That all free men do what is right on every occasion is a logically possible state of affairs.
- (5) God can create free men such that they always do what is right – (4), (3)
- (6) If God can create free men such that they always do what is right, and if God is all good, then any free men created by God always do what is right.
- (7) Any free men created by God always do what is right – (1), (5), (6)
- (8) No free men created by God ever preform morally evil actions – (7)
However, Alvin Plantinga (1971) has argued in response  that the propositions Mackie suggests are not “formally consistent; the resources of logic alone do no enable us to deduce an explicit contradiction from their conjunction” . The conclusion of Plantinga’s argument can be stated with the following proposition:
- (a) God is omnipotent, omniscient, and wholly good, and God creates free men who sometimes preform morally evil actions.
The Free Will Defense merely states that (a) is not contradictory or necessarily false. A further explanation of (a) would be to say that “[a] world containing creatures who are sometimes significantly free [ ... ] is more valuable, all else being equal, than a world containing no free creatures at all” .
So, consider the following: To show that some given proposition p is consistent with a proposition q is to produce a third proposition r whose conjunction with p is consistent and entails q. Interestingly, proposition r doesn’t need to be true or even known to be true (nor plausible), it just needs to be consistent with p and in conjunction with the latter entail q. The Free Will Defense then seeks to find such a proposition.
Leibniz and the Best of All Possible Worlds
Gottfried Leibniz in his Theodicy (1709)  argued that before he created the universe, God, “not content with embracing all the possibles, penetrates them, compares them, weighs them one against the other, to estimate their degrees of perfection or imperfection, the strong and the weak, the good and the evil [ ... ] [t]he result of all these combinations and deliberations is the choice of the best from among all these possible systems, which wisdom makes in order to satisfy goodness completely” .
Leibniz argues that God was confronted with a wide array of options in terms of possible worlds that he could have created. However, by virtue of his wisdom, goodness and omnipotence, God created this world, the actual world. Therefore, according to Leibniz, this world must be the best possible world. Now, Mackie sympathetically agrees with Leibniz’s premise that if God did create a possible world, it would be the best possible. However, Mackie simply rejects an omnipotent and wholly good God, since, it is evident that this is not the best possible world.
Plantinga on the contrary argues against both Leibniz and Mackie, questioning as to whether there is such a thing as the “best of all possible worlds,” let alone a best. It is rather that God, though omnipotent, could not have created any possible world that he pleased. What do he mean by this?
It should be noted that if something is created, there was a time before which it did not exist (i.e., at some time, a thing came into existence). Plantinga first suggests that God did not create himself, along with numbers, propositions, properties, or states of affairs (these did not begin at some point in time); however, it would be appropriate to say that God actualizes states of affairs (i.e, “his creative activity results in their being or becoming actual” ). So, God can actualize some given possible world Q if and only if he can actualize every contingent state of affairs associated with Q.
However, although there are a number of possible worlds where, for example, Abraham never met Melchizedek, God cannot actualize any of them. This is because Abraham in fact did meet Melchizedek, and so not even an omnipotent being can actualize the possibility of Abraham never meeting Melchizedek; it is too late for that. This is demonstrated by Plantinga’s point where he writes:
Take any time t; at t there will be any number of worlds God cannot actualize; for there will be any number of worlds in which things go different before t. So God cannot actualize any world in which Abraham did not meet Melchizedek; but perhaps God could have actualized such worlds. Perhaps we would say that God could have actualized a world W if and only if for every contingent state of affairs S included W, there is a time at which it is (timelessly) within his power to actualize S. 
Proceeding to the Suffering of Essences
Plantinga notes something he identifies as Transworld Depravity, which can in some sense be used in the Calvinist sense of Total Depravity. He explains :
(a*) A person P suffers from transworld depravity if and only if for every world W such that P is significantly free in W and P does only what is right in W, there is a state of affairs T and an action A such that
- (1) God strongly actualizes T in W and W includes every state of affairs God strongly actualizes in W,
- (2) A is morally significant for P in W, and
- (3) if God had strongly actualized T, P would have gone wrong with respect to A.
Thus, significant usage of transworld depravity is that if a person suffers from it, then it was “not within God’s power to actualize any world in which that person is significantly free but does no wrong – that is, a world in which he produces moral good but no moral evil” . Now, it is clearly possible that everyone suffers from transworld depravity, however, if this given possibility were in fact actualized, then “God could not have created any of the possible worlds that include the existence and significant freedom of just the persons who do in fact exist, and also contain moral good but no moral evil” . To do this very thing, God would have had to have created people who were “significantly free” but suffered from transworld depravity. The consequence of this possible world would be that such persons would produce moral good as well as moral evil.
It should be noted that this doesn’t complete the argument for the Free Will Defender. From the fact that all people in some possible W suffer from transworld depravity it doesn’t follow that God could not have created a world containing moral good without moral evil. According to Plantinga, God could have created other people. “Instead of creating us, he could have created a world containing people all right, but not containing any of us” . This is where Plantinga invokes instead of Persons, Essences.
Plantinga and Essence Simpliciters
An essence simpliciter can be understood as
- (ex.) a Property P such that there is a world W in which there exists an object x that has P essentially and is such that in no world W* is there an object that has P and is distinct from x.
Thus, before invoking a new proposition from (a*), it should be understood that E is a person’s essence; also that, if this is so, this person is the instantiation of E – i.e., “he is the thing that has (or exemplifies) every property in E” . To instantiate an essence, God creates a person who has that essence, thus, in creating a person he instantiates (or represents) an essence. Thus, our new proposition (b*) can be lead to say that:
(b*) An essence E suffers from transworld depravity if and only if for every world W such that E entails the properties is significantly free in W and always does what is right in W, there is a state of affairs T and an action A such that
- (1′) T is the largest state of affairs God strongly actualizes in W,
- (2) A is morally significant for E’ instantiation in W, and
- (3) if God had strongly actualized T, E’s instantiation would have gone wrong with respect to A.
This is a far more respectable thesis since that transworld depravity is an accidental property of those essences and persons it afflicts. Thus, when we noted from the beginning that if we have a pair of propositions p and q whose truth are jointly consistent there is a given proposition r whose conjunction with p is consistent and entails q. Thence, we can employ the following:
- (c*) Every essence suffers from transworld depravity.
(c*) is consistent with God’s omnipotence, and is clearly consistent with (1): God is omnipotent, omniscient, and wholly good. Thus, the conjunction of (1) and (c*) show that
- (d*) God actualizes a world containing moral good.
This conjunction of (1) and (c*) is consistent, and thus entails (2): There is evil. Therefore, Plantinga’s argument is successful.
-  From God and the Problem of Evil, ed. William L. Rowe (Blackwell Publishing: 2001) p. 124
-  Ibid., p. 125
-  Ibid., p. 124
-  J H.J. McCloskey, God and Evil in Philosophical Quarterly, 10 (1960) p. 97
-  J.L. Mackie, Evil and Omnipotence, Mind 64 (1955) pp. 200-212
-  Quoted from Rowe, p. 78
-  Mackie (1955), p. 209
-  Alvin Plantinga, God and Other Minds, 2nd edn. (Cornell University Press: 1992) pp. 136-137
-  Alvin Plantinga, The Nature of Necessity (Oxford University Press: 1971) see pp. 164-93
-  Quoted from Rowe, p. 92 – Plantinga’s emphasis.
-  Quoted from Rowe, p. 93
-  Gottfried Leibniz, Theodicy, Essays on the Goodness of God, The Freedom of Man and the Origin of Evil (Routledge: 1951) see pp. 264-273, 377-388
-  Quoted from Rowe, pp. 7-8
-  Ibid., p. 95
-  Ibid., p. 96
-  Ibid., p. 112
-  Ibid.
-  Ibid.
-  Ibid.
-  Ibid., p. 113