What are semicolons?
Semicolons (;) separate independent clauses that are related in meaning, and they separate items in a list when those items themselves are long or include commas. For example, this summary could say “Semicolons are useful; they show that clauses are related in meaning.”
Semicolons Separate independent Clauses
A semicolon separates related independent clauses that are joined without a coordinating conjunction, such as and:
Mabel the Cat had made a big pot of goulash; it was simmering on the stove.
Goulash was Harry the Dog’s favorite; the scent drew him to the kitchen.
A semicolon can also replace a comma between two clauses that are joined by a coordinating conjunction like and in cases where the sentence might otherwise be confusing—for example, because of particularly long clauses, or the presence of other commas:
As Mabel’s culinary efforts continued, with bread baking in the oven and a cabbage dish just begun, she admonished Harry to keep out of her way; but Harry’s ability to remain at a decent distance from the stove was severely challenged.
Semicolons are used especially when the second clause is introduced by an adverb or a short phrase, such as however, indeed, thus, in that case, as a result, on the other hand, for example, or that is:
Mabel did not take kindly to the encroachment of Harry into her personal cooking space; indeed, she at one point responded to the sudden appearance of his muzzle at her elbow with a distinct and species-approspriate hiss.
Semicolons Separate Phrases or Items in a List or Series
A semicolon is used in place of a comma to separate phrases or items in a list or series when the phrases or items themselves contain commas or are especially long:
Harry set out to find a dessert that would demonstrate his deep appreciation of Mabel’s meal. Ideally, it would be sweet, salty, and chocolatey; would feature the soft, creamy texture that Mabel adored; and be suitable for breakfast as well as dessert.
Harry’s three favorite bakeries are in Pittsburgh, PA; Phoenix, AZ; and Walla Walla, WA.
When the items in a series are long or are sentences themselves, they are usually separated by semicolons even if they lack internal commas:
In the end, the meal Mabel and Harry shared was first-rate: the bread and cabbage dish complemented the goulash exquisitely; the chocolate croquembouche was divine; and the conversation was lively and amicable.
Merriam Webster