Here’s my problem with Lib’s argument:
Logic, whether modal or propositional, is a game. A symbolic game. I define symbols. I define rules. I create long strings of symbols. I manipulate them. I observe what happens to them. Etc.
The real world, the world we experience, the world we see and touch and feel, is something else entirely. It is, at its lowest level, a raw data stream that our brains process, and which we have learned to categorize as “light”, “sound”, “touch”, “chairs”, “the SDMB”, etc.
Now one of the most, perhaps the most, important discovery in human history is that taking the symbolic game of logic and applying it to the world is a very useful thing to do. I take the abstract symbolic logic-game called “numbers” and it gives me a powerful tool for predicting how many tomatoes I will have if I put all the tomatoes in my left hand and all the tomatoes in my right hand into a bowl. I take the symbolic games of logic and statistics further, and I end up with the Scientific Method, which has been observed over and over again to be able to predict things. This leads to inventions, discoveries, and enormous amounts of human progress.
But still, logic games are just games. Symbols. They have no actual existence. They exist only inside their own rigidly defined system.
Which brings us to the present discussion. Lib is familiar with a variation of logic called “modal logic”. I don’t know much about it (although I read through the Stanford page that he linked to), but I’m perfectly willing to believe that it is an internally consistent. Modal logic is, as I understand it, an extension of the more familiar “propositional logic” which has been the basis of logic and mathematics for centuries. One of the features of modal logic is that it includes symbols named “it is necessary that” and “it is possible that”. These symbols (and remember, they are just symbols in a game) seem, intuitively, to have correlations to concepts in the Real World.
Lib now invents a new symbol in Modal Logic. Let’s call it G. He gives G a definition inside Modal Logic. He then applies the (consistent) rules of Modal Logic, and determines that by those rules, inside the context of Modal Logic, G is true. (“True”, in this context, is a Modal Logic Word. The fact that there is an also a word in the English language “true” which corresponds to a Real World concept of truth is, at this point, irrelevant.) I have no quibble with his right to invent this symbol, define it how he pleases, and manipulate it inside Modal Logic World.
Now comes the troubling part, however. Lib makes two additional claims. It is very important to note that these are not Modal Logic claims. In fact, these are not (as far as I know) rigorously defined claims of any sort. In fact, they are just plain old assertions. They may be assertions that various famous philosophers from the past/present have agreed upon, and argued for at great length, but as far as I’m concerned, they’re just assertions. I will call them L1 and L2. (L2 is meaningless without L1).
** L1: Modal Logic is able to relevantly model, and make predictions about, the real world.** In fact, it is able to do so so well, it can produce not just predictions, but absolute proofs, about the real world. And in fact, the Modal Logic concept of truth corresponds precisely with the real world concept of truth, and the Modal Logic concepts of “it is possible that” and “it is necessary that” correspond precisely with their intuitive, English-language, real world equivalents.
L2: Within the context of the Modal Logic – Real World correspondence established in L1, Lib’s concept of G is exactly equivalent to the real world idea of God.
I challenge Lib (or anyone else) to make a case for either L1 or L2. The problem with L1 is that not all consistent symbolic games are at all useful when it comes to describing and predicting the real world. For instance (very simple example here) it’s perfectly possible to do all of one’s math modulo 9. That is, 8+1 = 0. This is a perfectly consistent system. And in fact it will give you all sorts of nice useful results. But it will also tell you that if you have 4 apples and then 5 more, you’ll end up with no apples. The mere fact that modal logic is a consistent logical game, and an outgrowth of propositional logic, in no way convinces me that I should use it to describe or predict the real world (although honestly, this is a very confusing and subtle topic).
It’s easiest to criticize L1 and L2 together. L2 wants to set up a correspondence between a concept in the real world (God) and a concept in logic-world (G). Of course, setting up such correspondences is necessary and useful, and no science could ever be done without such correspondenes. For instance, suppose I wanted to predict how two billiard balls will bounce off of each other. I first learn the rules of the logic-game called Classical Newtonian Mechanics. I then come up with a way to set up correspondences between billiard balls on a table and hypothetical concepts of CNM. I then observe that the rules of CNM allows me to predict, with incredible accuracy, where the billiard balls go. Thus, I feel confident in my claim that CNM was a useful way to describe billiard balls (L1) and my analysis of what concepts in CNM correspond to billiard balls, and how (L2).
I didn’t just randomly assert “hey, Modal Logic is a useful, and in fact, perfect, way to discuss real world questions of theology and cosmology, and God corresponds perfectly to G”. I might as well say “hey, parabolic functions are a perfect way to describe absolute Evil, and this particular one here corresponds perfectly to Sloth.”
One last thing (and this is venturing more into imho territory than GD territory): I’m not aware of any situation in science, math, or philosophy in which a logical/symoblic game has been by-consensus-succesfully used to describe, predict, and/or prove a concept anywhere near as amorphous and ill-defined as “God”. In fact, although I am an agnostic, I think it cheapens one of the most profound ideas in all of human thought to say “well, this concept is so simple that it can be described, predicted, and proved by the rules of a game so simple that they can be described on a web page in 10 minutes”. Any concept of God that can be 100% encompassed and described by a symbol in a logical game is not one that lives up to the passion and depth of the human religious experience.