In the English language, we have two ways of expressing purpose: 'to' and 'so that'. Examples: I am walking to the shop to buy some milk; I am walking to the shop so that I may buy some milk. However, in Latin we have four different ways of making a purpose clause. The most common way is 'ut' plus the subjunctive - the present subjunctive is used when the main verb is in the present or future tense, whilst the imperfect subjunctive is used when the main verb is in the past tense. A negative purpose clause uses 'ne' instead of 'ut', meaning 'so that...not'. We also see the relative pronoun qui, quae, quod being used to express purpose. Just as with 'ut', these clauses also use the subjunctive mood. A less common way of expressing purpose is 'ad' with the gerundive. However a gerundive is easy to identify due to the distinct -nd eg. 'mittendus'. You are most likely to be asked to identify a purpose clause using ut/ne plus the subjunctive at this level.