What is a gerund and how is it used?

The simplest way of describing a gerund is to call it a 'verbal noun', that is, a noun formed from a verb. Another way might be to describe it as the 'noun of an action'. For example, if we have the verb 'portare' - 'to carry', where 'portare' is the infinitive (literally meaning 'to carry'), its gerund would be 'portandum', which we could translate literally to 'the act of carrying'. The gerund, as you might imagine, is always neuter, and so declines like 'bellum, -i', i.e. a 2nd declension neuter noun. It has several uses which make it very useful for Latin prose composition, as well as being easy to spot in translation with its unique '-nd' endings. 1) It can be used in the genitive with 'causa (abl.) or gratia (abl.)' to mean 'for the sake of...' e.g. causa/gratia fugiendii - 'for the sake of fleeing' 2) It can be used in the accusative with 'ad' to mean 'for the purpose of...' e.g. ad fugiendum - 'for the purpose of fleeing' 3) It can be used alone in the ablative to denote many things, such as its being instrumental e.g. discederunt fugiendo - 'they left by fleeing'. As you can see, these structures make it ideal for a simple prose composition such as the one you can opt for in your A-level exam, especially as a substitute for an 'ut + subjunctive' purpose clause. Its formation is very straightforward. With 1st conjugation verbs such as 'portare' it becomes 'portandum', with 2nd and 3rd conjugation verbs such as 'habere' and 'monere', they become 'habendum/monendum', and with 4th conjugation verbs 'audire', it becomes 'audiendum'. N.B. it is important to not get confused between the gerund and present participles and more confusingly, the gerundIVE, which looks similar but has different uses and constructions. The most important difference to remember is that the gerund is a verbal NOUN, whereas the present participle and the gerundive are both ADJECTIVES. This means that the gerund will never agree with any nouns around it, it stands on its own substantivally.