a recipe calls for 4 cups of bread flour can i use all purpose flour instead?

It drives me just a little bit wild when recipes written for home cooks call for bread flour or all-purpose flour, as though the two are interchangeable. They're not, they're just not. What are you making? If a bread, I'm sorry to be the bearer of bad tidings, but if you try to make it with all-purpose flour, you won't be happy with the results. AP flour simply does not contain enough protein (gluten) to both literally hold up a loaf of bread and allow you to slice it without it breaking. Here is some information about different baking flours that might help you:
http://thesolitarycook.wordpress.com/2012/02/12/ciabatta-the-bread/
http://thesolitarycook.wordpress.com/2012/02/01/lets-bake-bagels-part-1/
http://thesolitarycook.wordpress.com/2012/01/22/rustic-italian-bread/

We might be able to help you better if we knew what you are making.

I'm assuming this is a bread of some sort. In general, yes, all purpose flour will do in a pinch, but don't expect the best results that you could get for crumb and lift. It should still be edible, if that's what you mean.

You can certainly use all purpose flour for pizza dough. But the best is a high gluten flour.