Weapons have explicitly listed hardnesses and hit points:
Many medieval weapons were known for breaking; most notably, in jousting, breaking a lance scored points:
Given that in D&D we often have impressive characters using unimpressive weapons (think weapons sized for Medium creatures used by Large creatures, or a 30 strength score), it seems to make sense to me that striking might logically break your weapon, but I'm not sure if that's in the rules.
From a strictly balance perspective, there might be uses for weapon breakage:
Then again, the rules explicitly reference sundering as a way of breaking a weapon:
And from a DMing perspective, it seems like it would be a lot of extra bookkeeping.
What's the right way?
For Clarification
I have seen fumble rolls break weapons, and leather armor go bad after a rainstorm if not maintained in games. That's different.
I'm referring more explicitly to attacks. If a weapon is used to attack, does it suffer damage, which if beyond the weapon's DR, could take away its hit points? Over time, this would result in a broken weapon, but not right away.
Best Answer
No.
RAW, no, weapons do not break themselves. Only damage explicitly done to objects via sundering or striking an object apply. The rules in Damaging Objects are the sum of how you can do it; if it's not there it's not there for a reason. They also don't say your weapons don't disintegrate every Tuesday, "it doesn't say it doesn't happen" is not a logical argument about a ruleset.
Furthermore, lances aren't more fragile than any other two handed wooden hafted weapon in Pathfinder. (Nor were they fragile in real life - jousting lances were specially hollowed but ones for real fighting were as sturdy as anything else.)
You can house rule that damage applies to weapons - but given the inflated damage numbers of Pathfinder, weapons will be breaking on every hit. Over level 3 hits routinely do 15+ points of damage per strike and that would explode a lance or spear or halberd every time. So then you'd need to do "half damage" or something and it becomes a logistical challenge. Note that weapons become "broken" at half hit points and provide a penalty and are completely destroyed at 0 hp. If implementing a weapon damage rule, I'd take it to a more realistic level; maybe do 1d6 damage to it on a natural 1 (or maybe a number equivalent to the hardness of the thing being struck).