TULIP (aka: Canons of Dordt)
These are the five main points arrived at at the Synod of Dordt (1618-1619) in response to controversial challenges and objections made by Arminian thinking to the teachings of John Calvin (who is suggested by many to be the best expert, of his time and otherwise, of systematic theology). Simply put, though, these points pretty much sum up what Christians believe in about how salvation works. Some “Christians” don’t think these beliefs are true (e.g. we don’t need to be forgiven or Jesus’s death was only a formality), but these are all founded on Biblical doctrine, so we sort of have to question whether or not someone can call themselves a Christian and deny the Bible’s authority–clearly, no, not really.