What is a purpose/final clause?

Constructions in Latin are not as terrifying as you may think; it's just a case of learning the grammatical rules for each construction and putting them into practice. 

A purpose clause indicates the reason for which a certain action was done. As with other constructions, the verb found in a purpose clause will always be subjunctive. If we were to use a purpose clause in English, the verb would be an infinitive (I went to the shops to buy some groceries). 

The Latin purpose clause will be made up of 'ut' (=in order to), or 'ne' (=in order to not) and the imperfect subjunctive (-rem, -res,-ret, -remus, -retis, -rent)

Consider the following example:

denique ego ad patrem redii ut rem explicarem.

Finally I returned (perfect, 1st person ending) to my father in order to explain the matter.

More literally: Finally I returned to my father so that I could explain the matter. 

If the purpose clause is negative (i.e. not to do something), we use the conjunction 'ne' instead of 'ut'. Consider the following example:

noctem exspectavimus ne ab hostibus videremur. 

We waited for night in order to not be seen by the enemy. 

Or, we waited for night so that we wouldn't be seen by the enemy.

(NB. the Latin word 'hostis' (enemy) is nearly always written in the plural form, so expect to find 'hostes' or 'hostibus' frequently)

So, to recap:

* A purpose clause is used to express a reason for why an action has been done;

* The imperfect subjunctive is always used (because the verb is still a possibility, it hasn't happened yet so we can't use an indicative verb);

* Purpose clauses are always made up of the conjunctions: 'ut' or 'ne', and the imperfect subjunctive;

* It's worth learning your verb endings of the imperfect subjunctive so that these constructions are easy to spot in unseen translations.