Dear American Heritage Dictionary, 4th edition (2009):
Hello! How are you? Ahem. It has recently come to my attention that your definition of Founding Father (capitalized) reads thusly: "A member of the convention that drafted the U.S. Constitution in 1787." Now, as you may know, Thomas Jefferson did not attend the Constitutional Convention, occupied as he was in France, furthering the new nation's interests and buying many many nice things. Therefore, according to your definition, Thomas Jefferson is not a Founding Father. I would urge you to say that aloud to yourself a few times. Doesn't it sound silly? Yes it does.
My point there, of course, is that it was not necessary to be physically present at the Constitutional Convention to have had a profound role in the formation of the new United States. And anyway, I'll have you know that, even though he wasn't physically present, our man TJ was busily sending Little Jimmy Madison crates full of books so he could do some hard-core homework on how to write a constitution.
And lest you should think me purely offended on behalf of Thomas Jefferson, you are in fact also excluding John Adams and Patrick Henry. Gunning Bedford, Jr.: Founding Father. John Adams, Patrick Henry, and Thomas Jefferson: not Founding Fathers.
So in closing, American Heritage Dictionary, 4th edition (2009), I urge you to revise your definition of Founding Fathers. It is arbitrary and nonsensical, and what's more, people in various blogs and columns and Letters to the Editor are constructing odd arguments based on its dubious authority as we speak. This is not to be borne. I would suggest something more inclusive. Something like the Oxford English Dictionary's very reasonable "an American statesman of the Revolutionary period, esp. a member of the American Constitutional Convention of 1787."