Tiles move and break because there is too much deflection in the subfloor. It moves. Tiles don't. Tiles break. The cure is to increase the stiffness of the subfloor. That can involve additional layers of plywood over the existing subfloor, the sistering of joists to be stronger, the intermediate bracing between the joists, and an uncoupling membrane. Or a combination.

Your floor should be rated at L720 to be able to use natural stone. Enter in the values of your flooring system in the the Deflectolator That will tell you if your floor is strong enough. If won't tell you what to do if it's not. But, all of that will need to come up in order to remedy the situation. It has to be redone.

I'd suggest finding a CTI Certified installer for the remedy.

I'm sorry but the installer of the tile needed to check the deflection rating (as The Cook's Kitchen points out) for you.

The hint that something had to be ADDED: what was on the floor originally? Was it sheet vinyl? Carpet? What used to be there?

And plywood subfloors really must be SPECIFICALLY BUILT to handle tile. If the original house "came" with sheet vinyl, then the builder would have built a subfloor that could handle sheet vinyl (relatively light weight floor). If the house came with ceramic tile, then the builder would have made the subfloor rigid enough for tile.

In a way, your tile guy was right (the original build was NOT designed for the weight of tile) and in a way s/he is wrong because it was her/his responsibility to give you feed back on the deflection rating of the existing subfloor so that you - the homeowner - could give him/her the GO AHEAD to ADD more rigidity (ie. add more layers of plywood until it met the right deflection rating...which means you would have to spend more money on the subfloor preparation).

Just for fun, why don't you pull out your old contract and see how much money you paid for subfloor preparation. If it says $0.50/sf, then you got nothin'. If it says $3/sf then you PAID for the preparation but didn't get $3/sf worth of work.

It is the second situation ($3/sf) that you are looking for. This is one of the few ways you can get the contractor to cough up the money to help you deal with this problem. If you PAID for the prep but didn't get it, you have a right to go after the contractor. If you did NOT pay for it, then you "got what you paid for" = nothin'.