Substantive and substantial are quite a pair: the two have multiple similar meanings, can both ultimately be traced back to the same Latin root (the verb substare, whose figurative meaning is best understood as “to stand firm” or “to hold out”), and both made their first appearance in English sometime in the 14th century. But though they can be used interchangeably in some contexts (one can make “substantive progress” or “substantial progress,” for example), we usually use substantial to describe things that are large in size, scope, or extent (e.g., “a substantial amount,” “substantial increase”), while substantive is more likely to be used as a synonym of significant, real, or important. Substantive change, for example, is change that makes a fundamental difference, regardless of its size. Substantive also functions in grammar-related contexts describing or referring to nouns and noun phrases.