We use a comma(,) to separate various thoughts or elements within a sentence. The core idea is to give a breathing pause when going through those different factors.
1. As a mark of parallelism, we use it to separate more than two items of a list.
E.g. Tom, Dick, and Harry.
2. Separate two ICs with a comma and fanboys
e.g. I went to London on May 24 last, and the British PM resigned on the same day
3. To separate a DC that starts a complex sentence from the main clause that follows.
e.g. When I went to London last, the British PM resigned.
4. To separate an adjectival modifier from the main clause.
e.g. Starting from the month of October, the festival season is a busy period in India.
5. To separate an adverbial or an absolute modifier
e.g., The principal admonished the ragging students, warning them of dire consequences
6. To use in a parenthesis between two commas to enclose additional but not essential information.
e.g.The Maya, famed for their the building skills, were natives of Mexico and Central America
7. To separate days and months and years, cities from their states or countries in reports. (Not of much significance to GMAT)
e.g., Sunday, Oct 20, 2019
e.g., Vadodara, India, based Reliance Industries is a mammoth conglomerate.
The semicolon (;) is used to connect two ICs that have some kind of relatedness. Sentences using a semicolon are compound sentences.
e.g., My mother came to stay with me for a few days; my wife left for her mother's home for those days.
We use a colon (:) after an IC to express, explain, or emphasize what the IC seeks to do. The statement after can be a word, or a phrase or a DC or an IC.
e.g., He was planning to take four tests: GMAT, GRE, LSAT, and TOEFL.
e.g., He wanted to fulfill his lifetime dream: wanting to join Harvard
e.g., After protracted efforts, she fulfilled her fondest desire: a house in Los Angeles.
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