Natural theology is a philosophy constituting the realm of Christian theology that is found in nature by excluding divine revelation in holy scriptures as authority. Appeal to the authoritative truth from the Bible is called revealed Christian theology and it forms theological doctrines about the nature of God. This is achieved by exegesis of verses found in the Old Testament and New Testament in regard to Jesus Christ for example. Alternatively natural theology bases itself within the realm of strictly observation in the natural world so that authority is given explicitly to nature as a way to know theology. The assumption is that the human mind is rational and able to know or understand nature, but only because a rational mind created nature. Philosophical argumentation and scientific evidences is the means by which natural theology can be articulated and systematized, not to falsify specific theories as such but to probe the nature of nature. To show logically that inference to transcendent mind over matter is the necessary being God.
Natural theology may begin with reason and observation rather than divine texts as authority but both are an epistemology about the nature of God.
Plato (427–347 BC) in Book VII of The Republic expounds upon an imaginative story that intends to capture how the mind, the intellect or the soul is illuminated by revelations found in nature. Plato depicts human beings since childhood shackled in a dark cave, even their legs and necks chained disabling them the ability to merely turn their heads. Above and behind them a fire “blazing at a distance”, and yet there is still more to this allegory because in-between the fire and the shackled prisoners are marionette players carrying all sorts of figurines, vessels and objects made up of different materials. These cast strange and mysterious shadows to the shackled prisoners. These prisoners are confined strictly to see only that which the fire casts a shadow upon, their knowledge of the world is limited like the darkness of shadows seen and thought to be the only thing existing by limited experience. The imagery by Plato is then articulated by supposing an echo came from the other side of the cave, and inferring that the prisoners would posit the voice had come from the shadows.
And suppose further that the prison had an echo which came from the other side, would they not be sure to fancy when one of the passers-by spoke that the voice which they heard came from the passing shadow? 
The allegory of the cave by Plato climaxes when the prisoners are released and emerge into the world outside. The prisoners are led and guided by an instructor who attempts to educate them as their sight adjusts to reality they never knew. They are guided by the instructor and they can only gaze for moments at the surroundings and outlines of objects by way of the shadows. Not able to fully comprehend the breathtaking beauty of the world outside by sight. The sun is far to bright to even glimpse at yet. The prisoners adjust more and more and are reluctantly led up to where they may fixate toward the heavens and ultimately at the sun. The light source from which gives all life it would seem. The sun illuminates the reality of the world for the once prisoners, and that is the Form of the Good. It is a new stage of understanding initiated through education in light of the Good. It leads from mere sensory exploration of humans into knowledge of the form of the Good. The form of the Good essentially can be seen as the cause of why there is something (being and thus knowledge) rather than nothing (non-being) called the first principle by Plato.
And now look again, and see what will naturally follow it’ the prisoners are released and disabused of their error. At first, when any of them is liberated and compelled suddenly to stand up and turn his neck round and walk and look towards the light, he will suffer sharp pains; the glare will distress him, and he will be unable to see the realities of which in his former state he had seen the shadows; and then conceive some one saying to him, that what he saw before was an illusion, but that now, when he is approaching nearer to being and his eye is turned towards more real existence, he has a clearer vision, -what will be his reply? And you may further imagine that his instructor is pointing to the objects as they pass and requiring him to name them, -will he not be perplexed? Will he not fancy that the shadows which he formerly saw are truer than the objects which are now shown to him?
Certainly. He will then proceed to argue that this is he who gives the season and the years, and is the guardian of all that is in the visible world, and in a certain way the cause of all things which he and his fellows have been accustomed to behold?
Clearly, he said, he would first see the sun and then reason about him. 
Plato however envisions an impersonal representation of the Good. The language attempts to personify the sun but Plato did not ground concepts like justice or morality into that nature of the Good. They remain as abstract objects and intrinsically relative within his works. William Lane Craig, a Christian philosopher, takes direct issue with this essential of Platonism considering it a deficiency.
What is deficient in Plato’s theory is a person who can issue moral imperatives as an expression of the Good; but that want is supplied by theism. So it seems to me that Divine Command Theory’s derivation of an “ought” from an “is,” far from being objectionable, captures a central feature of moral duty and plausibly grounds it.
Aristotle (384–322 BC) in Physics through observation of natural motions concluded a first mover of things, a force unmovable who set things into motion. In a later writing called Metaphysics Aristotle identifies the unmoved mover as separate from matter and its nature that of a disembodied mind.
Plato and Aristotle were two ancient philosophers that uncovered two distinct ways to investigate reality and truth. There was firstly “poetic-mythological-theological” or what can be called revealed theology in modern terms, and secondly the rational human mind that starts and ends with observation in nature (natural theology).
During medieval philosophy arguments for God without relying on revelation underwent considerable exploration producing many different paths spurring many timeless debates still central to natural theology today. Anselm of Canterbury in the 11th century and Thomas Aquinas in the 13th century made great strides with natural theology inside of the western philosophical tradition. The first published philosophical writings in English were that of natural theology called The True Intellectual System of the Universe by Ralph Cudworth (1617–88).
According to The Blackwell Companion to Natural Theology in the essay entitled “The Project of Natural Theology” by Charles Taliaferro natural theology played an important role in the development of modern philosophy;
Natural theology played a major role in early modern philosophy. Some of the classics in the modern era, such as the Meditations by Descartes (1596–1650), An Essay Concerning Human Understanding by John Locke (1632–1704), Three Dialogues between Hylas and Philonous by George Berkeley, the Theodicy by Leibniz (1646–1716), the Dialogues Concerning Natural Religion by David Hume (1711–76), and the Critique of Pure Reason by Immanuel Kant(1724–1804) all constitute major contributions to assessing reasons for and against theism, without making any appeal to revelation.
The cosmological argument is a family of arguments within natural theology that demonstrate the existence of a “Sufficient Reason or First Cause” for the cosmos from apparent self-evident facts. Inasmuch as the metaphysical concept of God is classic theism or un-caused and non-contingent, and essentially good the rational inference leads inexorably to Him as the personal First Cause. The First Cause does not always mean the first of events in a long line of events into the past. The cosmological argument argues for a fundamental non-contingent cause that endures all contingent things at every moment regardless if there is a beginning or not.
Intelligent Design (ID) refers to a theory of origins or a scientific research program. In addition, the term is used to describe the community of philosophers, scholars, and scientists who are seeking evidence of design in nature. The scientific theory of intelligent design holds that;
certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection. 
ID theorists draw exclusively upon empirical evidence to support the existence of a creative intelligence or designer. ID purports that design can be detected without any understanding of who the designer is or why the agent acted, or even how the phenomenon in question was actually produced. ID is a unique scientific position that stands in stark contrast to naturalistic, materialistic philosophy of science which puts forth abiogenesis rather then intelligent agents as the main mechanism that created biological systems for sustaining life. It can also clearly be distinguished from religious creationism in that it stakes no claim regarding the specific identity of the creator, nor does it use references from scripture when forming theories about the history of the world. In fact, many ID theorists support the idea of common descent and billions of years of time. ID simply postulates that certain features within the cosmos present clear evidence of being deliberately and intelligently designed.
Views on God
The predominant forms of natural theology in philosophy today are theistic and deistic natural theologies.
Theism is the religious philosophy that asserts God exists and that He created and sustains the cosmos. Classical theism states that the creator God not only exists but is omniscient, omnipresent, exists necessarily, nonphysical, eternal and essentially good. The most competitive alternative philosophy within the modern intellectual climate is metaphysical naturalism, a philosophy of science acting without the existence of God and the soul, preceding with the assumption of strict materialism.
Deism is the theological position that God created the world, but then left it to run without any divine intervention. It rejects all miracles and divine revelation and asserts that religion should be derived by reason alone. This was a common position of Enlightenment thinkers, although naturally it has no support from the Bible.
- ↑ 1.0 1.1 1.2 The Blackwell Companion to Natural Theology Edited William Lane Craig and J. P. Moreland, 2009 Blackwell Publishing Ltd. ISBN: 978-1-405-17657-6
- ↑ The Epistemology of Religion By Stanford Encyclopedia of Philosophy. First published Wed Apr 23, 1997; substantive revision Wed Mar 11, 2009
- ↑ 3.0 3.1 Book VII. The Republic by Plato
- ↑ Question 165, Subject: Does Theistic Ethics Derive an “Ought” from an “Is”? Response by William Lane Craig
- ↑ Natural Theology. 1. Historical Beginnings of Theology and Philosophy Internet Encyclopedia of Philosophy
- ↑ Philosophical Foundations for a Christian Worldview, “The Existence of God” By J. P. Moreland and William Lane Craig. pg 465
- ↑ Cosmological argument by Stanford Encyclopedia of Philosophy
- ↑ The Theory of Intelligent Design: A Briefing Packet for Educators p6. by Discovery Institute. November, 2007.