How do I spot a purpose clause?

A purpose clause contains a main verb in the indicative, and a secondary verb in the subjunctive which is introduced by 'ut'. If the main verb is in the past tense, the imperfect subjunctive is used. ie. servus ad forum festinavit ut cibum emeret. (the slave hurried to the forum in order to buy food)Alternatively, the subjunctive can be introduced by the part of the relative pronoun (qui, quae, quod) which corresponds to the subject of the verb in the subjunctive. ie. dominus servum ad forum missit qui cibum emeret (the master sent the slave to the forum, who was to buy food / in order to buy food)Negative purpose clauses are expressed with 'ne' instead of 'ut'. ie. puer epistulam celavit ne mater eam videret (the boy hid the letter so that his mother would not find it)