Substantival possessive pronouns are used on their own and cannot be used to describe a noun, playing the role of noun phrases, so mine may stand for "my cat", "my sister", "my things", etc. In some languages these may require articles or other determiners, as the French le mien etc. In English, the -'s possessives formed from nouns or noun phrases can be used in the same way; the president's may stand for "the president's office", "the president's policies", etc., as determined by the context.