Most of the parts of speech are fairly easy to grasp—nouns are things that can serve as subjects or objects, verbs are things that usually denote actions or states of being, and so on—but some are a little more slippery.
Take gerunds and participles, for instance. Maybe you know that there are both present and past participles, and maybe you know that some of these words have -ing endings and some don’t, but maybe you’re like a lot of people and can’t quite keep them all straight. The good news is that it’s not as hard as you might think.
Gerunds and participles are both derived from verbs and can function as other parts of speech. Gerunds function as nouns, while participles cover several different functions. Past participles of regular verbs look just like the past-tense form: walked, laughed, baked. Past participles of irregular verbs, though, take different forms, sometimes changing the vowel and sometimes adding an -en on the end, as in done, sung, eaten. Past participles can function as adjectives (as in the broken clock) or as adverbs (as in Stunned by the loss, I didn’t know how to react, where the participial phrase stunned by the loss modifies the verb in the main clause). They can also be combined with have to form the perfect tenses (as in The clock had stopped or My phone has died) and with be to form the passive voice (as in The clock was knocked off the wall or My phone was killed when I dropped it in the cats’ water dish).
Present participles are formed with an -ing ending, and, like past participles, they function as adjectives (as in the sleeping baby) or as adverbs (as in Reading it again, I can see how it’s confusing). They can also combine with be to form progressive constructions (as in The baby was sleeping).
Gerunds are formed with an -ing ending, so they look just like present participles, but they function as nouns, as in Reading is fun or She likes reading, where reading is a subject of one sentence and the object of the other. In other words, the basic distinction between gerunds and present participles is that gerunds function as nouns, while present participles do everything else.
And because gerunds and present participles are so similar, some linguists have argued that they’re really the same thing—a single form that can function as nouns, adjectives, or adverbs or as parts of verb constructions. They call this form the gerund-participle. After all, they argue, gerunds and present participles look identical—they’re both formed by adding -ing to a verb. There is not a single verb for which the gerund and present participle are different. And participles already serve several different functions, so why not just say that present participles and gerunds are really just one form that can function in several different ways?
There’s a good historical argument for this too. The gerund and present participle used to be completely distinct in Old English, with the gerund ending in -ung or -ing and the present participle ending in -ende. In Middle English, these endings merged together to yield a single form, -ing, for both present participles and gerunds. The only reason we’ve traditionally considered them distinct in English is that they were distinct in Latin, and analyses of English grammar were heavily influenced by Latin grammar. But there’s no reason why we should still be beholden to Latin grammar. English isn’t that closely related to Latin, and anyway, Latin’s been dead for centuries. Why should we continue imposing the Latin model on English if it doesn’t make sense?
So if you want to stick to traditional grammar, just remember that gerunds function as nouns and that everything else is a participle. But if you want to wow your coworkers with your cutting-edge knowledge of English linguistics or you just want to “well, actually” someone, you might consider embracing the more modern view and acknowledge that the gerund and present participle are really just one form filling multiple roles. You’ll be doing the language a favor.