A really solid argument may need even further support, especially if what we’re arguing is complicated. Warrants, remember, explain the way our grounds support our claims. The next task, however, is to be able to show that we can back up what we have claimed by showing that the reasons we have given for a claim are good reasons. To establish that kind of further support for an argument is to provide backing.

What is appropriate backing for one kind of argument might be quite inappropriate for another kind of argument. For example, the kinds of reasons relevant to support an amendment to the Constitution are completely different from the kinds appropriate to settle the question of what caused the defeat of Napoleon’s invasion of Russia in 1812. Arguments for the amendment might be rooted in an appeal to fairness, whereas arguments about the military defeat might be rooted in letters and other documents in French and Russian archives. The canons (established conventions) of good argument in two such dramatically different cases have to do with the means that scholarly communities in law and history, respectively, have developed over the years to support, defend, challenge, and undermine a given kind of argument.

Another way of stating this point is to recognize that once you have given reasons for a claim, you are then likely to be challenged to explain why your reasons are good reasons — why, that is, anyone should believe your reasons rather than regard them skeptically. They have to be the right kinds of reasons, given the field you are arguing about. Why (to give a simple example) should we accept the testimony of Dr. X when Dr. Y, equally renowned, supports the opposite side? What more do we need to know before “expert testimony” is appropriately invoked? For a different kind of case: When and why is it safe to rest a prediction on a small though admittedly carefully selected sample? And still another: Why is it legitimate to argue that (1) if I dream I am the king of France, then I must exist, whereas it is illegitimate to argue that (2) if I dream I am the king of France, then the king of France must exist?

To answer challenges of these sorts is to back up one’s reasons, to give them legitimate backing. No argument is any better than its backing.