Plain English

A gerund is a verbal noun--that is, a form of a verb which functions grammatically as though a noun. Gerunds can be the subject of a verb, a direct object, the object of a preposition, and so forth. Because a gerund is a verbal, however, it retains some features of a verb, namely voice (active vs. passive) and the ability to govern a direct object.

It should be noted that infinitives are also verbal nouns, though they can generally only function as subjects or direct objects.

The big problem in English is that gerunds are identical in form to present active participles: both end in "-ing." So it is imperative to note with the greatest of care whether an "-ing" word is functioning as an adjective, in which case it is a participle, or as a noun, in which case it is a gerund. For example:

Riding a bike in the rain is a good way to get soaked.

What is the subject of the sentence--i.e., what's a good way to get soaked? "Riding a bike in the rain"--a gerund phrase, consisting of the gerund itself ("riding"), its direct object ("a bike"), and a prepositional phrase ("in the rain").

 

A very large truck nearly squashed the boy riding in the rain.

Notice here that "riding" is no longer functioning as a noun. Instead, if we should ask "Which boy did the truck nearly squash?", you would say "the one riding in the rain," which proves that we have here a participial phrase which modifies the noun "boy."

Plain Latin
A gerund is formed from the present stem of a verb, to which are added the letters -nd- and then the endings of the second declension neuter singular, thus:

	1st	2nd	3rd	3rd -io	4th
GEN.	parandi	monendi	regendi	capiendi	audiendi
DAT.	parando	monendo	regendo	capiendo	audiendo
ACC.	parandum	monendum	regendum	capiendum	audiendum
ABL.	parando	monendo	regendo	capiendo	audiendo

Note these peculiar features:

• in 3rd -io & 4th conjugation, you have two vowels (-ie-) instead of the stem vowel;
  there is no plural (true also in English; no one would say "I admire your skillful drivings."
• there is no nominative; this is because Latin uses the infinitive for a verbal noun functioning as the subject of a sentence.
• all Latin gerunds are to be translated as active

Case-usage for gerunds follows that used for common nouns, and they will be found in the four cases with fairly similar frequency. Consider these examples:

1. iuvenes audiendo Brutum excitati sunt.

The young men were stirred up by hearing Brutus.

 

2. Quintus amorem scribendi numquam amisit.

Quintus never lost his love of writing.

 

3. Caesar bibendum vitat.

Caesar avoids drinking.

 

4. occasio pugnandi mox aderit.

An opportunity for fighting will soon be here.

 

BUT...
5. fugere a proelio est turpe.

To flee from a battle is disgraceful.
(Since the verbal noun is the subject of the sentence, Latin uses an infinitive rather than a gerund.)