Adding to Vulture's reply (that you can not make absolute positive statements about truth), the modern view of "Occam's razor" (at least in Bayesian thought) is the minimum description length (MDL) principle (http://en.wikipedia.org/wiki/Minimum_description_length), which can be rigorously formalized. In this formalism, it becomes a prior over models. Multiplied with the likelihood over models (derived from data), this gives you a posterior. In this posterior, if you have two models that make exactly the same predictions, the simpler one is preferred (note that the more complicated one isn't completely rejected; it's just given lower posterior probability).

There are very deep fundamental theoretical considerations for why MDL is a very good way of assigning a prior to beliefs. If someone wants to reject Occam's razor, they would have to give an alternative system and show that under the assumptions of MDL it gives better long-term utility. Or that the assumptions of MDL are unfounded.