Purpose Clauses: To, In Order To & So As To
Level B1 · Verb Patterns
To explain why someone does something — their purpose or goal — English uses to + infinitive, or the more formal in order to / so as to + infinitive. She left early to catch the train, She left early in order to catch the train, and She left early so as to catch the train all answer the question 'why did she leave early?' with the same meaning, but in order to and so as to sound more formal and are especially useful when to alone might be misread as part of a different structure.
How to build a purpose clause:
- to + base verb is the simplest, most common way to express purpose in everyday speech and writing: I called to ask about the schedule; We saved money to buy a new car.
- in order to and so as to + base verb are more formal alternatives, common in writing, and especially useful at the start of a sentence: In order to succeed, you must work hard; So as to avoid delays, arrive early.
- For a negative purpose (doing something to avoid a result), only in order to and so as to can take not before the infinitive — plain to cannot: She whispered so as not to wake the baby; He left early in order not to be late (never to not be late in this formal pattern).
- for + noun (not + infinitive) is used only when the purpose is expressed as a thing or activity, not an action with its own subject: I went to the shop for some bread (not to buy for some bread); to express the action itself, switch to the infinitive: I went to the shop to buy some bread.
The most common mistake is using for + infinitive to express purpose — I went to the shop for to buy bread is wrong in standard English; drop for and use to alone: I went to the shop to buy bread. A second mistake is putting not before to in the negative purpose pattern — to not wake the baby is common informally but the traditional formal pattern places not after to: so as not to wake the baby, in order not to wake the baby.
Ask yourself why someone does something, and check whether the answer could start with 'in order to…' or 'so as to…' — if so, you're looking at a purpose clause, and plain to + infinitive usually works too. For a negative purpose, look for not right after in order/so as, not right after a bare to.