The ordinary reasoning we encounter in real life is usually incomplete and often confused.  Rational reconstruction is a painstaking attempt to interpret a person's reasoning so that it is as complete and unconfused as it can possibly be.  You've noticed how difficult this is, and probably thought it a bit strange that you should have to work so hard to interpret reasoning that often seems to have been put together rather carelessly. You might also think it pretty odd that the rationales we construct are somehow supposed to capture the meaning of what was originally said.  After all, most people reason without any knowledge of how to construct rationales themselves.

We often do talk about the act of interpretation as if it is an attempt to grasp the true and original meaning of what someone has said.  This can be a useful way to think about it when the reasoner seems to have a clear and authoritative grasp of the matter at hand.  But a rational reconstruction is really not an attempt to discover an originally intended meaning.  As with any other form of speech, people typically reason without fully understanding what they are saying. The original reasoning provides the content and the basic logical relationships, but its meaning is really indeterminate until it has been clarified to the point that it succeeds in communicating something. 

When we rationally reconstruct a person's reasoning we attempt to arrive at an interpretation that makes the most sense from a logical point of view.   Logical interpretation is just one form of interpretation, and it can be usefully compared to others.  We interpret facial expressions, physical gestures, stories, poems, sounds, signs, experiences, dreams, fortunate and unfortunate events.  Is the point of, say, literary interpretation to capture the original intended meaning of a work? Some people think so, but it's a tough view to defend.  After all, if we want to know the intended meaning of a poem, why wouldn't we just ask the author?  The reason is that the author doesn't actually get to decide this sort of thing.  Of course, we'll probably give her interpretation more significance than others, but what makes a literary work powerful and worth talking about is that it can generate different satisfying interpretations at different levels to different people. Even if the author had some original meaning in mind, we don't have to care that much. What counts in the end is what it means to us.

Interpreting reasoning is similar in some ways, but different in others.  When we adopt the logical point of view we really don't think the ability to generate multiple interpretations is such a wonderful thing.  Ambiguity is a literary tool, but (as we'll see below) it is a logical failing. On the other hand, as with literature, we don't accept the author's perspective as completely authoritative, either.  This isn't because all interpretations are equally interesting. Rather, it's because, in the language the author is using, words have conventional meanings, and these meanings determine unambiguous logical relationships, even if the author himself didn't intend them. It makes perfect sense to ask an author if your particular reconstruction is based on a charitable interpretation of what he originally said.  But she really is not in a position to decide whether her reasoning is subject to the logical relationships depicted therein.

The Principle of Charity in Interpretation

A good rational reconstruction almost always ends up being a compromise between what the reasoner actually said and what would make the most sense from a logical point of view.  A good rational reconstruction will not compromise the original reasoning, but it will often reformulate what a person said in clearer, more logically satisfying way.  When we proceed in this manner we are following the Principle of Charity in Interpretation.  You can think of this as a kind of logical Golden Rule:  Interpret unto others as you would have them interpret unto you.  Of course this formulation works only for people who always want to be interpreted from a logical point of view, and few do.  So our Principle of Charity is better stated:  Always interpret the reasoning of others so that it makes the most sense from a logical point of view.