Three years ago I started the Natural Religion Study Group at the American Philosophical Association's Pacific Division. I took the name from David Hume's Dialogues Concerning Natural Religion, and thought it more appropriate given the APA setting than the title Natural Theology. We have had three years of very interesting presentations.
The question that is asked in Natural Religion is what can be known about God and the good through the use of reason to understand general revelation. Hume's answer is a skeptical one. Much of the consensus since his time, both among believers and unbelievers, is to accept his conclusion. Believers see it as proof of the need for blind faith, and unbelievers see it as proof that religion should be rejected.
In his study of Calvin, Benjamin B. Warfield took note of Calvin's view of Natural Religion. Much has been made of Calvin's reliance on the sensus divinitatis, including at Princeton Theological Seminary where Warfield studied and taught. This sense of the divine was linked with common sense and the assertion made that everyone knows God so that theistic arguments are nice but not necessary.
And yet Calvin, and those at Princeton, did give interesting analysis of theistic arguments. I'd like to consider a passage here in which Warfield studies Calvin's consideration of what is eternal. I do this because this is the most basic metaphysical question that can be asked, and so is the central question of Natural Religion: what is eternal?
"In developing this statement of the external natural revelation of God, Calvin presents first His patefaction in creation and then His patefaction in providence, and under each head lays the primary stress on the manifestations of the divine wisdom and power. But the other attributes which enter into His glory are not neglected. Thus, under the former caption, he points out that the perception of the divine power in creation 'leads us to the consideration of His eternity; because He from whom all things derive their origin must necessarily be eternal and self-existent,' while we must postulate goodness and mercy as the motives of His creation and providence" (B.B. Warfield, Calvin and Calvinism, 40).
It is formally true that whatever is the origin of all other being must itself be eternal and self-existent. To argue otherwise is to argue that all being is temporal, with beginning, and therefore came from non-being. What Calvin does here is lays the grounds for knowing God from Natural Religion. If we know that what is eternal is not material, but is a spirit (and therefore personal/conscious), we can argue to the goodness and mercy of God (those mentioned by Calvin above, although I'd say knowledge, power, and goodness).
Hume's argument against this is based on what has come to be called Hume's Fork. Hume said that all knowledge is either of the relation of ideas or sense data. The former tell us nothing about existence. Applied to arguments about God, the contention is that the above considerations about eternality have to do with the relations of ideas and therefore do not tell us about existence.
As an empiricist, Hume must go in this direction. What empiricism misses is that reason applies to both being and thought. In my book "Clarity" I demonstrate how Hume had the tools to see this. In his Treatise he did affirm that what is a contradiction cannot exist. Therefore, if it is shown that being from non-being is a contradiction, then there must have existed something from eternity. If it can be shown that what is eternal is not material, then the alternative must be true which is that what is eternal is a spirit. We can proceed in a similar fashion to theism.
This is Natural Religion. I'd like to argue that we need not end in Hume's skepticism. Rather, we can come to know some things about God and the good.