Is rational belief possible or are they two contradictory terms?

Isaac Franck in A Philosopher’s Harvest, Georgetown University Press, 1988 page 36 discusses how one deals rationally with Mekubalot – Beliefs that we receive through Tradition. He suggests that is what Rambam is saying in MN 1:50 when he says:

“For belief is only possible after the apprehension of a thing; it consists in the conviction that the thing apprehended has its existence beyond the mind [in reality] exactly as it is conceived in the mind.”

The way Isaac Franck puts it: He (Rambam) then proceeds to state his view on the relation between Reason and Faith in what, from a philosophico-methodological point of view, I am inclined to consider the most important passage in the Guide:

"If in addition to this we are convinced that the thing cannot be different in any way from what we believe it to be, and that no reasonable argument can be found for the rejection of the belief or for the admission of any deviation from it, then the belief is true."

In other words among the mental activities of human beings is the activity we call Belief. Through this activity we apprehend certain data. We are convinced that corresponding to our belief – state there is a belief- object which has its existence in reality exactly as it is apprehended by us. In addition to this knowledge through Belief there is knowledge through Reason. It is incumbent on us to examine all our Beliefs thoroughly in the light of Reason, and if we find them to be in conflict with reason i.e. to be absurd we must discard them.

Rambam had no patience with those who start with their beliefs and then attempt to justify these beliefs. The task as he saw it was almost the opposite. We must examine our beliefs in the light of Reason, and we must honestly attempt almost to disprove them. In the course of this process of critical examination, we may find that our beliefs are supported by Reason or by Natural Law, as in the case of the existence of God. When such support or verification is found, we of course accept it; but then the emphasis must be on Natural Law and on the scientific validity of the proof and of the ground for our belief. When Reason disproves our beliefs we must discard them as superstition.

If in the course of our thoroughgoing examinations we can find no reasonable argument for rejecting our belief, if we find that science and logic break down and cease to be relevant to the belief under consideration (e.g. Creation ab-nihilo in time), only then may we hold on to our belief with clear conscience even though we cannot supply any logical proof of its truth.

I believe that it is a very important point that needs to be made to all who try to rationally understand Judaism and its beliefs. In matters that are accepted on belief, when religion proposes an ontological explanation for an observation of a phenomenon, one must make sure it is such an explanation and not an empirically provable opinion. If it is not, one must make sure it is not in conflict with reality and only then can it be confidently accepted as true.

When we discuss what is referred to as “metaphysics”, we are talking about things that cannot ever be proven. They are outside the physical realm though they are related to it. For example if we were asked to prove empirically that God created the universe in time from nothingness, we could not do it. That question deals with something that happened at the moment when nothingness turned into something. That moment is at the exact finite instant time itself began. All we can do is see if it is not in conflict with observations that we can ascertain. If it does not conflict, we can then rely on tradition from revelation and accept it as true.
(See MN2:25 for a great read with this point in mind).