This document discusses different ways to express purpose in English using prepositions and infinitives. It explains that "in order to" and the infinitive form of a verb can be used to answer the question "Why?" and give the purpose of an action. It also notes that "for" followed by a noun phrase can similarly express purpose, but using "for" plus an infinitive or gerund form would be incorrect. Examples are provided to illustrate correct and incorrect usage of these constructions for expressing purpose.