The cosmological argument asks questions about the origin of the world around us. If we accept the idea that everything depends on something else for its existence then by continually regressing back we will arrive at the first cause behind all things, which exist today. This fact is assumed by both Christians and scientists, who argue that the world and everything in it exists because of a 'first cause'. Scientists would argue that the first cause was the Big Bang (Evolution). Christians (and other theistic religions) believe God (or the Divine) was the first cause of all there is (Creation). The cosmological argument not only seeks to reason the existence of God but could also be said to provide a meaning to life in the world. For instance, if we know where we have come from then surely, it could be argued, we have some idea of where we are going? Theists could claim that if life begins with God then life has a purpose with God. However, atheists could argue that if life began from a series of natural causes then the purpose to life must be found in biology.
St. Thomas Aquinas is considered by many to be the greatest scholastic theologian of the middle ages. Aquinas was a writer and wrote commentaries on most of the books of the Bible. His most famous works are 'Summa Theologica' and 'Summa Contra Gentiles'. Both the 'Summa Theologica' and 'Summa Contra Gentiles' are highly dependent of the philosophical thought of Aristotle. Aquinas' theological method was similar to Aristotle’s. Following Aristotle (referred to by Aquinas as the philosopher) he taught that philosophy is based on data available to everyone. Theology is based on revelation, for Christians, the Bible and logical deduction (reason) from revelation. An example of his use of philosophy in theological discourse is his famous 'Five Ways' ,which are an attempt to prove God's existence on the basis of what can be known from the world.
An example of one such 'proof' is The Cosmological Argument. Using Aristotle's notion of an unmoved mover he reasoned that one could argue back from the things we see in the world around us to a first cause or Great Designer – God. In his work Summa Theologica Thomas Aquinas offered five 'proofs' for the existence of God. As with Catholicism today Aquinas believed it was possible to discern truths about God based on reason (human rationality) and revelation (divinely revealed truths not available to reason). Aquinas lived at a time when Aristotle's teachings were popular and so used this as basis for his writings. Most notably had argued that things which changed required an unchanging source, an unmoved mover. This idea can be particularly seen in the first three of Aquinas' 'proofs' and forms the basis of what has come to be known as the for the existence of God. The fourth of his proofs has connections with what has been called the whilst the fifth way has been incorporated in what is called the (also known as the Teleological Argument). Throughout his arguments Aquinas assumes the existence of a God who is uncreated and independent of the universe and it's processes. God is not reliant on the world and the universe for God's existence however, the world and the universe is dependent on God for its existence. Without God there would be no universe or world.
Aquinas' 'five ways' are set out in the following way:
THE FIRST WAY: Everything in the world changes. Aquinas' argument here needs to be understood against the background of Aristotle's discussion of astronomy. Aristotle argued that planetary motion, which caused the seasons to change required an unmoved mover who would maintain the order of things. Aquinas used this notion to speak of the sustaining work of God. Thus without God the heavens and the earth would not exist. Aquinas described motion as “the reduction of something from potentiality to actuality” e.g. FIRE (actually hot) changes WOOD (potentially hot) Aquinas took this idea from Plato.
THE SECOND WAY: The notion of cause and effect means you cannot have the latter (effect) without the former (cause - here called efficient cause (which refers to that which brings another thing into existence or causes something to change)). There cannot be an endless regression of cause and effect thus there must be a first cause, which is God.
THE THIRD WAY: Things exist in the world but they need not. There was a time before certain things existed and there will be a time when they no longer exist. There must also have been a time when nothing existed. Objects have contingent existence (they can or cannot exist) but only God has necessary existence (God must exist). Thus if God did not exist nothing else would exist.