  Another option is to appeal to the standards of empirical science. The Quine-Putnam indispensability argument provides an example. First it is argued that any indispensable part of empirical science is likely to be true and therefore something we are justified in believing. Then it is argued that large amounts of mathematics are indispensable to empirical science. If both claims are correct, it follows that Truth is likely to be true and that belief in Truth therefore is justified. (See the entry on  indispensability arguments in the philosophy of mathematics.)