Here is an argument for the existence of God:

1. If there is a God, then it is very likely that there is a book that was written many centuries ago that is purported to be a divine revelation, and that is widely known about, and that is filled with nothing but true facts and wisdom and clear and sound moral guidance, and that provides great help for people to live good and happy lives.

2. If there is no God, then it is very unlikely that there is a book that was written many centuries ago that is purported to be a divine revelation, and that is widely known about, and that is filled with nothing but true facts and wisdom and clear and sound moral guidance, and that provides great help for people to live good and happy lives.

3. There is a book that was written many centuries ago that is purported to be a divine revelation, and that is widely known about, and that is filled with nothing but true facts and wisdom and clear and sound moral guidance, and that provides great help for people to live good and happy lives.

Therefore:

4. Other things being equal, it is probable that God exists.

I chose to structure this as a probability argument rather than as a modus ponens, but the saying ‘One man’s modus ponens is another man’s modus tollens.’ (a lovely skeptical principle) can be applied here, in a manner of speaking.

The first two premises seem plausible to me, but premise (3) is clearly false. So, the tables can be turned, and this argument can be reformulated to be used as a reason for rejecting or doubting the existence of God:

1. If there is a God, then it is very likely that there is a book that was written many centuries ago that is purported to be a divine revelation, and that is widely known about, and that is filled with nothing but true facts and wisdom and clear and sound moral guidance, and that provides great help for people to live good and happy lives.

2. If there is no God, then it is very unlikely that there is a book that was written many centuries ago that is purported to be a divine revelation, and that is widely known about, and that is filled with nothing but true facts and wisdom and clear and sound moral guidance, and that provides great help for people to live good and happy lives.

5. There is no book that was written many centuries ago that is purported to be a divine revelation, and that is widely known about, and that is filled with nothing but true facts and wisdom and clear and sound moral guidance, and that provides great help for people to live good and happy lives.

Therefore:

6. Other things being equal, it is probable that God does NOT exist.

Obviously, premise (5) is controversial and will require a fair amount of support (including criticism of the Old Testament, the Quran, the Vedas, etc.). But I am quite confident that a strong case can be made for (5), and that a reasonable and open-minded theist could be persuaded by facts and reasons that (5) is true.