Final answer:
Fideists argue that Christianity is true solely on the basis of Faith, without reliance on rational or empirical evidence. Faith is seen as self-sufficient in justifying religious beliefs, contrasting with philosophical approaches that seek rational or empirical support.
Step-by-step explanation:
According to Fideists, the basis on which we should argue that Christianity is true is D) Faith. Fideism emphasizes the understanding that religious beliefs are often not supported by rational or empirical evidence and instead relies on the presupposition that faith is sufficient for justification of religious beliefs. This view contrasts with other perspectives, like philosophy, which often seeks inferential justification through reason or empirical evidence.
Philosophers like Augustine of Hippo have argued to blur the distinction between faith and knowledge, suggesting that many beliefs typically taken as knowledge are actually based on faith, as humans cannot empirically validate certain claims, such as knowing one's own parents. Moreover, in the context of moral values, the Euthyphro problem presents the dichotomy of whether actions are good because they are commanded by a deity or if the deity commands them because they are inherently good. Either case implies difficulties for theistic ethics when reason tries to understand the divine command.
Ultimately, the role of reason in religious belief varies among different schools of thought. While some theologians and philosophers argue that reason can partially or wholly justify religious belief, Fideists maintain that faith alone is the grounding of religious truth, particularly in the case for Christianity.