It's easy to confuse a gerund with a verb in the progressive (also called continuous) verb tense. For example, in a sentence that says, "I am running,” the word ending in “ing” is a verb. In the sentence "I like running," the word “running” is a gerund that describes an activity and functions as a noun. Participles that end in “ing” are used to describe other nouns, and therefore they are adjectives even if they are written like verbs. For example, in the phrase "running water," running is not an activity but a description of the word water, which is a noun.
Aside from being confused with a continuous verb that also ends in “ing,” adjectives can also end in “ed,” which makes it look like a verb conjugated in the simple past tense. Simple in this case means the verb is not accompanied by another verb and is only required to have the suffix “ed” to be used in its past tense form. For example, in the sentence, "We wrecked the car," the word “wrecked” acts as a verb, but if wrecked is used in this way, "The wrecked car was a write-off," placed immediately before a noun, it is acting as an adjective.
Participles only function as adjectives or as part of an adjective phrase and must follow the same grammatical rules as other adjectives. A participle must be placed immediately before the noun it is modifying. A gerund, however, is a noun and is a lot more flexible. When used in a sentence or phrase, a gerund can function as a subject, direct object, the object of a preposition or a subject compliment. This is one way to differentiate between these two parts of speech.
This phrase is often used as a source of comic relief but it is actually describing a common problem with participles. If a participle word or phrase is not placed as closely as possible to the noun as possible, and the noun or subject of the sentence is not clearly stated, then the participle is not properly anchored to the sentence. In other words, it is dangling. In the sentence, "After having dinner, the light was turned off," The subject of the sentence — who had dinner or who turned off the light — is missing.