Introduction
What is natural theology?
Natural theology is the study of God but apart from the use of any special or written revelation.
Does the Bible teach that such a thing is possible?
It does. Psalm 19 speaks to this.
How does Psalm 19 show the possibility of natural theology?
Because Psalm 19 teaches us the reality of general revelation.
General Revelation
What is general revelation?
This is revelation that comes to us unwritten or unspoken.
What does Psalm 19 say about this?
In the first half of this Psalm, David speaks about general revelation; in the second part, of special revelation.
The heavens are telling (cf here) of the glory of God; And their expanse is declaring (cf here) the work of His hands. (Psalm 19:1)
Furthermore, this declaring never stops. It goes on day after day and night after night.
Day to day pours forth speech, And night to night reveals knowledge. (Psalm 19:2)
Then, we are told that this revelation comes to us not in words or by a voice.
There is no speech, nor are there words; Their voice is not heard. (Psalm 19:3)
Finally, we are told of its extent. It reaches to the ends of the earth; there is no place under the sun which cannot access this revelation.
Their line has gone out through all the earth, And their utterances to the end of the world. (Psalm 19:4)
Then in the last half of the Psalm, David switches to speaking about special or written revelation.
The law of the LORD is perfect, restoring the soul; The testimony of the LORD is sure, making wise the simple. (Psalm 19:7)
So if there is such a thing as general revelation, then there must be such a thing as natural theology.
Yes, precisely. Every science has its source or the object of its study from which it draws its conclusions. The geologist studies the earth, the biologist studies the human body, the astronomer studies the heavens, etc. The theologian also has his source which is Scripture or special revelation. When doing natural theology, this source is changed to that of general or unwritten revelation.
What other Scriptures speak to this?
Paul teaches in Romans that even those without the written word of God still know God.
For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who suppress the truth in unrighteousness, (19) because that which is known of God is manifest to them; for God revealed it to them. (Romans 1:18-19)
Note here that God has made a revelation of Himself even to the Gentiles who do not have the written word of God.
What truths about God are those without the written word of God capable of learning? How far can such a person come?
Paul goes on in Romans 1 to teach that since the creation of the world, God’s attributes, His eternal power, and divine nature are able to be seen clearly from the things which God created.
In history, there are several examples of brilliant men who had no access to the word of God. Plato, Aristotle, and others never read Scripture as far as we know. Why is their “theology” nothing even remotely close to what the Scripture teaches?
Paul answers this question as well. Granted these men did teach the existence of a “god” and did correctly describe some of His attributes, but the vast bulk of their theology is utter nonsense. The reason for this is that those without God’s word are not neutral toward God. Paul teaches that they are holding down or suppressing the truth because they are under the control of sin.
For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who suppress the truth in unrighteousness, (Romans 1:18)
What are the arguments that give us evidence for the existence of a deity?
See here.