38 U.S.C. § 1523: Combination of ratings

(a) The Secretary shall provide that, for the purpose of determining whether or not a veteran is permanently and totally disabled, ratings for service-connected disabilities may be combined with ratings for non-service-connected disabilities. (b) Where a veteran, by virtue of subsection (a), is found to be entitled to a pension under section 1521 of this title, and is entitled to compensation for a service-connected disability, the Secretary shall pay such veteran the greater benefit.