What is the difference between a gerund and a gerundive?

This is something that I remember having to spend some time on in the run-up to my A Levels!

The difference between the two is normally described along these lines: "the gerund is a verbal noun, whilst the gerundive is a verbal adjective". However, that can be rather unhelpful!

Gerund (verbal noun): an easy way to think of gerunds is to think of activities ending in -ing (reading (legendum); playing (ludendum); running (currendum) are all gerunds). A separate point is differentiating these from participles, but that can be left till later. In Latin, gerunds decline like bellum, but only have singulars.

Gerundive (verbal adjective): these translate roughly as "to be x'ed", examples in English being "to be completed", "to be written up" or "to be run". Because the gerundive describes something that has to be "x'ed", it works like an adjective. And because it acts like an adjective, in Latin it declines like the regular adjective bonus,a,um. So we get faciendus,a,um (to be done); scribendus,a,um (to be written); and "currendus,a,um" (to be run).