Before we can answer Nick's question, we need to discern exactly what it is he's asking. If we take the literal meaning of the two terms it's difficult to find any relationship at all. Philosophy is the study of, or the search for, knowledge and wisdom, while faith is unquestioning belief. Some might say by these two definitions that the two have nothing in common. On the other hand, there is little doubt that as people consider various philosophies and the claims of Christianity it seems both seek both knowledge and wisdom, so let's take a quick look at the two.
Philosophy is concerned with ultimate reality and seeks to explain the underlying cause of life, behavior, and so on. Christianity also deals with ultimate reality and the causes of life, behavior, and so on. However, whereas philosophy is speculative, Christianity accepts as truth an underlying reality based on God. And though philosophy is concerned with behavior and ethics, it seems to emphasize knowledge and speculation, while Christianity emphasizes faith and behavior. So, although there are some similarities between philosophy and faith, there seem to be some significant and fundamental differences.
On the other hand, the practice of Christianity has been likened as a philosophy for centuries. Indeed, the collected sayings of Jesus make a particularly fine philosophy that can be compared to a number of existing philosophies. For instance, Jesus says, "But when you are invited [to a banquet], go and sit down at the lowest place, so that when your host comes, he may say to you, 'Friend, move up higher'; then you will be honored in the presence of all who sit at the table with you" (Luke 14.10). This sounds suspiciously like something one might hear from a good Taoist. Indeed, there are those who have speculated that Jesus adopted or adapted many Buddhist teachings, teachings that predated Christianity by many centuries. And the comparisons can go on and on. And yet, as a philosophy, the teachings of Jesus would be considered rather eclectic and similar in content to many other ethical philosophies.
Not that practicing Christianity as a philosophy would be a bad thing. Indeed, Christianity would benefit if more of the "faithful", i.e., those who claim they "believe," would actually practice Christianity as their philosophy of life. In the words of John Lenin, "Imagine all the people living life in peace." Indeed, by practicing the philosophical teachings of Jesus and applying them to life there would be an end to mass consumerism/over-consumption, the oppressed peoples of the world would be freed, there would be no racism, classism, or any other -ism, and the only competition we would have with each other would be over who could do the most good deeds.
But Christianity is more that a philosophy. Christianity is a faith. And as a faith, it requires a god, something generally missing from philosophy. There are many moral and ethical people in this world, and some of them are Christian. However, the practice of Christianity as a philosophy leaves out the best and most important aspect of the faith-a personal relationship with Jesus. And as much as philosophy speculates, there is no speculation when it comes to a relationship. It takes a clear leap-of-faith to be in a relationship with God. And when one is in a dynamic relationship with God, then the motivation to keep the "philosophies" or the teachings of Jesus is founded in gratitude, devotion, and love of God. Conversely, the only motivation for philosophy is reason and devotion to the philosophy itself.
So, what's the relationship between faith and philosophy? It seems to me that faith without philosophy lacks direction. But a philosophy without faith lacks substance. Perhaps one cannot effectively exist without the other.
