Thomas was born in Roccasecca, in the Aquino county of the Kingdom of Sicily (present-day Lazio region, Italy), circa January 28, 1225. Saint Thomas Aquinas (c.1225-1274) was a scholastic philosopher and Dominican whose work had an enormous influence both on the course of Christian theology and on the course of philosophy generally.
Before Aquinas' work, the dominant figure in Western philosophy was Augustine, who emphasized the principles of God's sovereignty and the importance of revelation. The translation of Aristotle's works threatened this, however, because it appeared to give primacy to individuals and their own knowledge. It was impossible to either suppress or ignore Aristotle, but no one was having much success with reconciling Aristotle with traditional Church doctrine.
It was Aquinas who was finally able to make Aristotle's philosophy "safe" for Christianity. According to Aquinas, both sense experience and revelation provided truths for human beings - and, because both are true, both will always agree and will never contradict. Sometimes there will be truths which can only be known through one or the other - however, at no point will even these independent truths come into conflict with one another.
The recognition that empirical senses and reason could arrive at the same truths as revelation helped in the development of "natural theology," or the attempts to prove the existence of God through reference to natural facts about the world rather than through reference to scripture. Aquinas is particularly well known for his "Five Ways," five proof for the existence of god which rely upon the use of reason and empiricism rather than revelation.
The arguments are designed to prove the existence of a monotheistic God, namely the Abrahamic God (though they could also support notions of God in other faiths that believe in a monotheistic God such as Sikhism, Vedantic and Bhaktic Hinduism), but as a set they do not work when used to provide evidence for the existence of polytheistic, pantheistic, panentheistic or pandeistic deities.
Thomas was a theologian and a Scholastic philosopher. However, he never considered himself a philosopher, and criticized philosophers, whom he saw as pagans, for always "falling short of the true and proper wisdom to be found in Christian revelation." With this in mind, Thomas did have respect for Aristotle, so much so that in the Summa, he often cites Aristotle simply as "the Philosopher." Much of his work bears upon philosophical topics, and in this sense may be characterized as philosophical. Thomas's philosophical thought has exerted enormous influence on subsequent Christian theology, especially that of the Roman Catholic Church, extending to Western philosophy in general. Thomas stands as a vehicle and modifier of Aristotelianism and Neoplatonism.
Thomas believed "that for the knowledge of any truth whatsoever man needs divine help, that the intellect may be moved by God to its act." However, he believed that human beings have the natural capacity to know many things without special divine revelation, even though such revelation occurs from time to time, "especially in regard to such (truths) as pertain to faith." But this is the light that is given to man by God according to man's nature: "Now every form bestowed on created things by God has power for a determined act[uality], which it can bring about in proportion to its own proper endowment; and beyond which it is powerless, except by a superadded form, as water can only heat when heated by the fire. And thus the human understanding has a form, viz. intelligible light, which of itself is sufficient for knowing certain intelligible things, viz. those we can come to know through the senses."
Thomas's ethics are based on the concept of "first principles of action." In his Summa theologiae, he wrote: