Deism is the notion that God started the world, and from that time on does not do anything but watch from a distance. When creatures act, only creatures act; God is not now doing anything. He is not now causally involved in present events. Christian deism is a qualified form of deism, for it allows for divine interventions here and there in the course of redemptive history. These would be the miracles that we see described throughout the Bible, as well as the life of Christ. This is still a form of deism, for it fails to recognize the present activity of God in sustaining and directing all things.
On the opposite side of the spectrum is what is called occasionalism. Occasionalism is roughly the notion that all events are caused only by God. Creatures are not actual causal agents, but only seeming casual agents. According to occasionalism, while it seems to me that I am picking up this book, actually God is the one picking up the book. God is giving me the illusion that I am the one picking up the book, but in actuality I am not a genuine causal agent.
The correct position is a middle position between these two. When a creature acts, God is also acting as a primary cause while the creature is acting as a secondary cause. William Carroll explains this well when he writes:
Aquinas shows us how to distinguish between the being or existence of creatures and the operations they perform. God causes creatures to exist in such a way that they are the real causes of their own operations. For Aquinas, God is at work in every operation of nature, but the autonomy of nature is not an indication of some reduction in God's power or activity; rather, it is an indication of His goodness. It is important to recognize that divine causality and creaturely causality function at fundamentally different levels. In the Summa contra Gentiles, Aquinas remarks that "the same effect is not attributed to a natural cause and to divine power in such a way that it is partly done by God, and partly by the natural agent; rather, it is wholly done by both, according to a different way, just as the same effect is wholly attributed to the instrument and also wholly to the principal agent." It is not the case of partial or co-causes with each contributing a separate element to produce the effect. God, as Creator, transcends the order of created causes in such a way that He is their enabling origin. Yet the "same God who transcends the created order is also intimately and immanently present within that order as upholding all causes in their causing, including the human will." For Aquinas "the differing metaphysical levels of primary and secondary causation require us to say that any created effect comes totally and immediately from God as the transcendent primary cause and totally and immediately from the creature as secondary cause."
This also applies to redemption. On the one hand, the deistic equivalent is Pelagianism, i.e. we [alone] are the agents of our own salvation. Christ was, at most, a good example. We get to heaven by our good works. On the other hand, the occasionalist equivalent is a form of monergism that rejects any causes of our redemption other than Christ alone. We get to heaven because of "Christ alone" (Solus Christus). Nothing we or anyone else does contributes to our salvation. Notice that both of those positions are forms of monocausalism. Either it is all man, or it is all God; these two positions are the redemptive equivalent of deism and occasionalism, respectively.
B.B. Warfield was a famous Presbyterian at Princeton Seminary in the early twentieth century. Here is a quotation from Warfield's The Plan of Salvation (the 1935 edition):
... the Council of Carthage of A.D. 417-418, which refused to be satisfied by anything less than an unequivocal acknowledgment that "we are aided by the grace of God, through Christ, not only to know but also to do what is right, in each single act, so that without grace we are unable to have, think, speak, or do anything pertaining to piety." The opposition between the two systems [i.e. Pelagianism and Augustinianism] was thus absolute. In the one, everything was attributed to man; in the other, everything was ascribed to God." (p. 30)
Warfield reasons that if without grace we are unable to do anything pertaining to piety, then everything must be ascribed to God. But neither Augustine nor the Council of Carthage were affirming monocausalism or occasionalism. There are different ways in which everything can be "ascribed to God". One way is occasionalism, of course. Another way is to acknowledge that all our existence and causal power comes from God, and all the goodness of our good acts comes from God. In this latter way, we are truly causal agents even when doing righteous deeds, but in the former way (i.e. occasionalism), we are not truly causal agents. My point is that occasionalism is not the only way to "ascribe everything to God", and if one insists that occasionalism is the only way to ascribe everything to God, then "ascribing everything to God" comes into conflict with the doctrine of creation, in which case God doesn't want us to "ascribe everything" to Him, for He wants us to believe that He created us, and that we are real agents, and not mere brains in a divine vat under the illusion of being causally efficacious agents.
Pelagianism dies hard; or rather it did not die at all, but only retired more or less out of sight and bided its time; meanwhile vexing the Church with modified forms of itself, modified just enough to escape the letter of the Church's condemnation. Into the place of Pelagianism there stepped at once Semi-pelagianism; and when the controversy with Semi-pelagianism had been fought and won, into the place of Semi-pelagianism there stepped that semi-semi-pelagianism which the Council of Orange betrayed the Church into, the genius of an Aquinas systematized for her, and the Council of Trent finally fastened with rivets of iron upon that portion of the church which obeyed it. The necessity of grace had been acknowledged as the result of the Pelagian controversy: its preveniency, as the result of the Semi-pelagian controversy: but its certain efficacy, its "irresistibility" men call it, was by the fatal compromise of Orange denied, and thus the conquering march of Augustinianism was checked and the pure confession of salvation by grace alone made forever impossible within that section of the Church whose proud boast is that it is semper eadem. It was no longer legally possible, indeed, within the limits of the Church to ascribe to man, with the Pelagian, the whole of salvation; nor even, with the Semi-pelagian, the initiation of salvation. But neither was it any longer legally possible to ascribe salvation so entirely to the grace of God that it could complete itself without the aid of the discredited human will -- its aid only as empowered and moved by prevenient grace indeed, but not effectually moved, so that it could not hold back and defeat the operations of saving grace." (pp. 30-31)
What is driving Warfield here? Monocausalism. That is why he conceives of any genuine participation on the part of the human will as detracting from (or in competition with) divine grace. And that is why he rejects the Council of Orange (529 AD), rejects Aquinas, and rejects the Council of Trent. Here's how Warfield is thinking. If the human will, even aided by prevenient grace, can say no to God, then the will, by saying yes to God, is contributing to salvation, and thus salvation cannot be "entirely" ascribed to "the grace of God". The hidden premise in Warfield's argument is that the only way for salvation to be "entirely" ascribable to "the grace of God" is if no other cause (than God Himself) is operative in salvation. The hidden premise, in other words, is monocausalism.
Warfield does not show awareness that God being the only cause of salvation is not the only way that salvation can be truly by grace alone. When we say "grace alone", we have to understand the term "alone" in its respect-to-whatness, i.e. its proper context. Otherwise "grace alone" would eliminate creation. The proper context for understanding "grace alone" is not the absence of creatures having real causal powers.
Consider the angels. As rational spirits, they were created with a free will, and thus with the privilege of being participants in their own creation through the completion of their creation, by choosing once and for all, for the rest of eternity, whether to be angels (those spirits who love God) or demons (those spirits who hate God). Because they were given a will, they were each thereby given the privilege and power of freely determining, in one monumental choice, the kind of being they would be for all eternity. God did not create them in their final state. To have done so would have taken from them the privilege and perfection (for a creature) of being a participant in their own creation, and thus the self-possession that belongs to those who are what they have chosen to be, insofar as that is possible. Choosing what one will be for eternity is the closest a creature can come to imitating God's act of creating, and that is why it is such a privilege, a privilege that non-rational creatures cannot receive.
Humans too, as rational beings, were each given a will, and are thereby given the privilege of being participants in God's act of creating. We do this not only through procreation, but also through our free choices, much like the angels, except that unlike the angels, we are all one species, and we are material beings and in time. That is why we are affected intrinsically by Adam's sin, and also why it is not the case that our first choice determines what we will be for all eternity. In the case of a human, what determines the state of the soul for all eternity is the state of that soul at the moment of death, whether there is charity (i.e. love for God) in the soul, or whether the soul is in the state of mortal sin. This life is our time of testing; there is no second time of testing in a life to come -- that would be the error of cyclical reincarnation. "It is appointed unto man once to die, and then the judgment." (Heb 9:27) All that is the philosophical background and context to understanding the gospel.
And thus it is the context for understanding "grace alone". Given that background, we can understand why being saved by "grace alone" does not mean that God alone is the causal agent of salvation, because gratia non tollit naturam, sed praesupponit et perficit (grace does not take away or destroy nature, but presupposes and perfects it). Grace is a divine gift that allows man to do what God created us to do through our nature, choose to love Him for all eternity. Grace does not take away man's free choice; grace gives to man the real possibility to freely love God, because without grace man cannot love God. But grace does not force man to love God, or bypass man's will in bringing man to a state of loving God, because that would be the equivalent of God creating man in a state of already loving Him, without the privilege of participating in the choice of his final state.
Monocaualism, you may see, makes this present life superfluous. God might as well have created us all in the final state, some in heaven forever, and others in hell forever. This present life, with our opportunities to love God or reject Him, to serve and obey Him, or to rebel against Him, makes sense only if monocausalism is false, only if our choices here make a difference for the life to come. This present life is for us the equivalent of what, for the angels, was their first and ultimate eternal choice: "Choose for yourselves this day whom you will serve. (Joshua 24:15) That is why Christianity (though not its monocausal or fatalistic aberrations) makes this present life meaningful and eternally significant. What we choose here in this life determines who we are for the rest of eternity. Atheism, monocausalism and cyclical reincarnation philosophies undermine the significance and meaningfulness of our present choices. Catholicism preserves the eternal significance of our present choices while maintaining that we are saved by grace alone, because nothing good that we do would be possible without God's grace, for in every good deed that we do, God is always at work in us, both to will and to work for His good pleasure. (Philippians 2:13)
Once we understand why monocausalism is false, then we see why the notion that either we are saved by Christ or by our works is a false dilemma. We can see why the notion that if Christ is the mediator between God and man, then no one else can be a mediator between Christ and man is a non sequitur. We can see why the notion that if Christ is forgiving our sins, then we must not need a priest to absolve us is a non sequitur. We can see why the notion that if Christ saves us, then the merits of the saints can do nothing for us, is a non sequitur. All these arguments are based on the hidden premise of monocausalism. Since tomorrow the Church celebrates the 2000th anniversary of the birth of St. Paul, let us consider something that he wrote.
Consider Colossians 1:24
Νῦν χαίρω ἐν τοῖς παθήμασιν ὑπὲρ ὑμῶν, καὶ ἀνταναπληρῶ τὰ ὑστερήματα τῶν θλίψεων τοῦ Χριστοῦ ἐν τῇ σαρκί μου ὑπὲρ τοῦ σώματος αὐτοῦ, ὅ ἐστιν ἡ ἐκκλησία,
Qui nunc gaudeo in passionibus pro vobis, et adimpleo ea, quae desunt passionum Christi, in carne mea pro corpore eius, quod est Ecclesia.
Now I rejoice in my sufferings for you [plural], and in my flesh I fill up the deficiencies of Christ's afflictions for His body, which is the Church.
Some people who do not know Greek think that St. Paul is saying that there are deficiencies in St. Paul's flesh which he [St. Paul] is filling up with the afflictions of Christ. Others claim similarly that by "deficiencies of Christ's afflictions" St. Paul is speaking of himself as united to Christ, and thus of the deficiencies in his [St. Paul's] own sufferings, which, because of the union of St. Paul with Christ, can thus in some sense be said to be deficiencies in Christ's-sufferings-in-St.-Paul. But these hermeneutical gymnastics are all necessitated by the presupposition of salvific monocausalism. The very idea that Christ's sufferings could be in some sense deficient or lacking for our salvation is, for salvific monocausalists, anathema.
St. Paul is talking about his own sufferings for the Colossians. He is saying that Christ's afflictions in His passion and death, though sufficient for their purpose, were not causally sufficient in themselves and by themselves to save the Colossians without the labors and sufferings of the Apostles, and particularly in this case St. Paul. St. Paul's suffering in the flesh for the Colossians is filling up what is lacking in Christ's suffering for His Mystical Body, the Church. In the Greek it is clear that the deficiency to which St. Paul is referring is a deficiency in Christ's afflictions, not in St. Paul's flesh. St. Paul is rejoicing that he gets to be a genuine causal agent in saving the Colossians. That in no way detracts from Christ's saving work, as though St. Paul's sufferings nullify or refute the fact that all grace comes to the Colossians through Christ and His saving work. Rather, through Christ's saving work, St. Paul himself has become an agent of salvation for the Colossians. Christ's saving work works in and through St. Paul, such that St. Paul's choices, labors, and sufferings truly and genuinely causally contribute to the salvation of the Colossians, while at the same time, everything that St. Paul does and gives to the Colossians comes from Christ who lives in St. Paul. (Gal 2:20) Once again, it is neither Christ to the exclusion of all other causal agents, or man alone. We do not have to choose between occasionalism or deism. Both are a form of monocausalism. Monocausalism is, fundamentally, a denial of the doctrine of creation, for agere sequitur esse (a thing acts according to what it is). And if God is the only actor, then there is no creation. And if nature is the only actor, then there is no Creator. The doctrine of creation necessarily holds together the genuine existence and causal agency of both God and creation.
Those who reject monocausalism are typically dismissed as 'synergists', which is viewed as some species of Pelagianism. (Think of Warfield's characterization of the position of the Council of Orange as "semi-semi-pelagianism".) In response to the charge of synergism, ask the person who is making the charge how he avoids both deism and occasionalism. Then ask him why his solution cannot also apply to salvation, if his position is not to be ad hoc. We should not be afraid of labels like "synergism" or Warfield's neologism "semi-semi-pelagianism". In order to evaluate what is under the label, we have to evaluate the *concepts* underlying the terms. Positions cannot be rightly evaluated on the basis of the labels alone, without unpacking those underlying concepts. If it turns out that when unpacking the concept, the 'error' of synergism is simply that it is not monocausalism, then it is time to call monocausalism into question. (See Dr. Phillip Cary's article "Augustine and the Varieties of Monergism".) It seems to me that in order for Protestants and Catholics to be reconciled regarding our respective doctrines of salvation, we have to confront the underlying philosophical disagreement regarding monocausalism. Otherwise we are talking 'above' the fundamental reason for our disagreement.
Lord Jesus, please help Protestants and Catholics to be reconciled and reunited, in one body, one Spirit, one hope, one Lord, one faith, one baptism, and one God and Father of us all. And please use my little work here as a genuine cause in that reconciliation and reunion. In the name of the Father, and of the Son, and of the Holy Spirit. Amen.