Relating Circular, Inductive, and Deductive Reasoning to the Scientific Method and Religion
Subjective beings with limited comprehensions of the universe must use specific examples to derive "generalities," i.e. broad understandings of concepts that can be reapplied to specific situations, in order to function. An inability to derive and reapply generalities would leave individuals incapable of reacting to novel situations without specific training, thus preventing humans from responding to real world events in real time.
That said, it is actually our subjective nature that results from our need to use inductive reasoning to function. Subject beings, who are fortunate enough to be trained to address various situations in an objective manner by transcending their bias, i.e. scientists, versus those trained to find common ties in order to bridge subjective perspectives, i.e. nonscientific philosophers, with limited knowledge of the universe, use both inductive and deductive reasoning to derive their general understandings of the world.
Furthermore, inductive reasoning allows us to develop generalized models that can be used to deduce specific predictions. While inductive reasoning is the inverse of deductive reasoning, the conclusions of inductive reasoning must be verified through deductive reasoning. In other words, people naturally use inductive reasoning to develop their understanding of the universe, but scientific thinkers use deductive reasoning to validate their conclusions. In essence, this is the scientific method stated in the most general terms possible.
This is not circular reasoning as different examples are used to induce a generalized model before those examples are used to deductively confirm the generalized model. Saying God exists, for example, because God exists is circular. Deriving the existence of God from events and circumstances is, however, an example of unverified inductive reasoning. In other words, proper examples of God's actions would be needed to use deductive reasoning to confirm His existence.
These proper examples may or may not exist, i.e. the hypothesis may not be testable, which is why religion is not scientific in nature. As such, the question of whether God exists or not is not a scientific question, because it is not testable. It is a philosophical question. It is not, however, circular reasoning; God is an idea derived from a subjective perspective that utilized inductive reasoning to arrive at the conclusion that God exists.
Unfortunately, it is only from objective, non-religious perspectives that this line of reasoning can be used as the subjective perspectives of religious thinkers have evolved to exclude the possibility that God does not exist. Again, this is not circular reasoning as the subjective perspective would cease to exist if another conclusion was reached and the thinking would be transformed into a different subjective perspective. Religious individuals simply make different assumptions about the unknowns of the universe than non-religious individuals, i.e. God exists versus God's existence is unknown.