This all assumes that your belief is actually true. How do you know this without falling into the trap of circular reasoning? That is to say, what outside the Bible stands as solid evidence to support only your belief and no other?
First of all, the problem of circular reasoning is often found among scientists:A '...geologist who has recognized the circularity problem is Dr. Ronald West, at Kansas State University.'
"Contrary to what most scientists write, the fossil record does not support the Darwinian theory of evolution because it is this theory (there are several) which we use to interpret the fossil record. By doing so, we are guilty of circular reasoning if we then say the fossil record supports this theory."
Anyway, as mentioned, the acid test which verifies a prophet as bone fide, initially comes from the Bible. All prophets which deviate from this, are false. The Bible sets the standard in the same way western science sets its own standards.
21 And if you say in your heart, 'How shall we know the word which the Lord has not spoken?' — 22 when a prophet speaks in the name of the Lord, if the thing does not happen or come to pass, that is the thing which the Lord has not spoken; the prophet has spoken it presumptuously; you shall not be afraid of him. (Deuteronomy 18:21-22; NKJV)
Arguably, using this verse to prove a prophet is true is not circular reasoning. A is true, so that does not mean that B is true. B could be true or false. A = the Bible, B being the prophet or prophecy. Circular reasoning says 'A is true because B is true' 'B is true because A is true. (http://en.wikipedia.org/wiki/Circular_reasoning
). If the prophet is potentially true, it is because he has met the criteria set out in the test, but it must be meaured by external evidence.
So, here comes the external evidence apart from the bible. If the prophet fits the criteria on paper so to speak, in line with the full biblical acid test, it is compared with actual world events, not necessarily listed in the bible. The prophecy could be verified by other sources, such as newspapers, tv programs etc. If the prophecy did not come to pass, then that person has failed. The external evidence outside the bible is vital if we are to increase our faith and understand the fulfillment of prophecy. What helps contribute to our faith in Gods prophets, is their track record as well.
Prophecy is not open to interpretation as God meant what He meant and not ten or a hundred other things. The Bible is clear what it means. When Daniel told the King of Bablylon, "You are the Head of Gold" it was clear what Daniel meat to us. It means Babylon is represented by the Gold head in the dream of the male image. When Daniel says another kingdom will come after Babylon and replace it, which was represented by Silver, we know that means the Medo Persians. In Daniel 5, this is clarified. So it continues. It is very specific. We have used external evidence i.e historical facts, sources and other items to prove that the Medo-Persians did infact take over Babylon, and then Greece, and then the divided kingdom of Rome.
Second, this is post hoc reasoning even so, because a false (but earnest) prophet can easily meet the conditions you described. The only way to tell if they are true or false is whether their prophecies come true or not.
A false prophet can not easilly meet the conditions I described. For example, how many prophets after Jesus, kept the 7th day Sabbath, kept all 10 commandments, believed Jesus was the Son of God, and all the other criteria within those basic outlines of the acid test, and got all their prophecies right? So, Mormons have a prophet who keeps and taught Sunday observance, therefore on that alone, he is a false prophet, no matter if all his prophesies came to pass. Prophets have to meet ALL criteria. The way to tell first off, which normally cuts them off straight away, is according to Isaiah 8:20.. To the Law and to the testimony, if the prophet speaks not according to this it is because there is no light in him. This means, included in the Law is the Sabbath teaching, so if the prophet does not teach and observe this law just as the testimony of the other biblical prophets agree, then we can discard him or her straight away as a false prophet. Joseph smith never taught the Sabbath, therefore he is a false prophet. Muhammed never taught the law either, i.e the sabbath, nor did he teach his followers to observe it, therefore he is a false prophet and so on. Thats even before we get to what they actually said.
Third, it is incredibly easy for a person to interpret prophecy to suit their whim. A prophecy that seems false could actually be shown to be true much later on, and a prophecy that seems true could actually end up being false (because people tried to manipulate events to make it come true). So how do you tell whether it's true or false when someone could come along later and show that a seemingly false prophecy was actually true, and a seemingly true prophecy was actually false?
Bearing in mind the above points, there is a whole host of other criteria as well. Since most christians and other faiths do not keep the Sabbath, which is part of the Moral Law of God, or the Ten Commandments, then prophecy for them will become very confusing and subjective in nature. If the prophet does not speak according to the law or the testimony (i.e teach what other biblical prophets teach concerning the law) of other biblical prophets, then he or she is no prophet of God.
In short, it's practically impossible to tell whether a prophecy was true or false.
I would disagree. Start by objectively looking at the biblical criteria, teach the law, teach what other biblical prophets teach, etc.. then we can build or close a prophets portfolio based on that... taking into consideration external evidence such as world events.
PS. A false prophet in terms of Christianity does not have to mean that he got all his prophesies wrong so he's a false prophet, as some false prophets have arguably made predictions which have come true. However, they never get all right, and often truth is mixed in with error. Thats why we have to conduct the full test and ask questions such as 'do they teach the law and observe the sabbath?' Most so-called prophets, fail this test. Psychics and mediums etc can get things right, but they often get things wrong as well. The key here is fulfilling Biblical criteria.