Those are only beliefs that are justified given certain prior assumptions and conventions. In another system, such statements might not hold. So, from a meta-logical standpoint, it is improper to assign probabilities of 1 or 0 to personally held beliefs. However, the functional nature of the beliefs do not themselves figure in how the logical operators function, particularly in the case of necessary reasoning. Necessary reasoning is a brick wall that cannot be overcome by alternative belief, especially when one is working under specific assumptions. To deny the assumptions and conventions one set for oneself, one is no longer working within the space of those assumptions or conventions. Thus, within those specific conventions, those beliefs would indeed hold to the nature of deduction (be either absolutely true or absolutely false), but beyond that they may not.