Not only are there two Korans, Meccan and Medinan, that are different in tone and subject matter, but also the Koran has many verses that contradict each other.
Koran 2:219 says that Muslims should be tolerant and forgiving to People of the Book.
Koran 9:29 says to attack the People of the Book until they pay the jizyah, the dhimmi tax, submit to Sharia law and be humbled.
Which verse shows the true nature of Islam?
The Koran recognizes its contradictions and even gives a rule to resolve the contradictions. The later verse abrogates (supercedes) the earlier verse. This does not mean, however, that the earlier verse is wrong or in error. This would be impossible since the fundamental hypothesis is that Allah created the Koran and, hence, the earlier verse must be true or Allah would be wrong.
Abrogation has an impact on the arguments about the true nature of Islam. At endless interfaith dialogs, the early tolerant verse is quoted to show the nature of Islam as being peaceful. When both verses are quoted and then abrogation is applied, we see that the later verse trumps the earlier tolerant one. Jihad abrogates tolerance. In general, the Medinan Koran abrogates the Meccan Koran. In the two verses above, tolerance is abrogated by jihad against the Christians.
But, the earlier verse is true and still used. Abrogation does not negate the early verse. Indeed, the earlier "peaceful" verse that is abrogated is the one most apt to be used in public discourse.
This creates a logical problem, since if two things contradict each other, at least one of them must be false. This is a fundamental element of Western unitary logic. In Koranic logic, two statements can contradict each other and both are true. This is dualistic logic.
An alternative explanation is that the early verse is first stage in a process, like a seed, and the later verse is a second stage, like a plant. There is truth to this, but the process model does not take into account the fact that both truths are available at the same time. To go back to the analogy, you don't have the seed and the plant at the same time. The verses contradict each other and are both true at the same time. This is dualistic logic.
The contradictions are usually explained by abrogation, the classical doctrine, but the principle of abrogation is limited to the Koran. Duality includes the special case of abrogation and it explains how the entire doctrine of Koran and Sunna work. It is not just the Koran that is contradictory, but all of the Sunna.
Another dualistic aspect of Islam is its ethics. One of the chief features of Islam is the doctrine of the Kafir. It treats them dreadfully and horribly. No one would ever want to be treated as a Kafir is treated in the Trilogy. This leads us to the Golden Rule. There is no Golden Rule in Islam because of the division of humanity into believer and Kafir. The Golden Rule is to treat ALL people as you would be treated. Since no one wants be treated like a Kafir, and the Kafir is so central to Islamic doctrine, it proves that Islam has no Golden Rule. Islam has one set of rules for Muslims and another set of rules for Kafirs. This is dualistic ethics. An example of the dual ethics is the subject of friends. The Koran has 13 verses that say that a Muslim is not to be a friend of Kafirs.