God's existence cannot be deduced by reason alone.
For nothing ought to be posited without a reason given, unless it is self-evident (literally, known through itself) or known by experience or proved by the authority of Sacred Scripture.
No more things should be presumed to exist than are absolutely necessary.
Entities should not be posited unnecessarily.
Whenever two hypotheses cover the facts, use the simpler of the two.
Entities are not to be multiplied beyond necessity.