swear by

Idioms  

1. Have great reliance on or confidence in, as in She swears by her personal physician . [Early 1800s]

2. Also, swear to . Have reliable knowledge of, be sure of, as in I think she was going to the library but I can't swear to it . [Mid-1700s]

3. Take an oath by, as in I swear by all the saints in heaven . [Early 1200s]

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Example Sentences

There’s a reason runners swear by pickle juice as a recovery drink, and why “pickle girls” have become their own corner of the internet.

From Salon • May 28, 2026

“At the end of the day, the government is going to go with systems that have been deployed, where combatant commanders swear by the fact that they want one of what we have,” Mengucci said.

From Barron's • Jan. 15, 2026

It’s true, some of the world’s top CEOs and elite athletes swear by early rising.

From The Wall Street Journal • Jan. 11, 2026

Some people swear by writing a song every day and finishing it, even if it’s bad.

From Los Angeles Times • Dec. 1, 2025

"But when I speak of the Lion of course I mean Aslan, the great deliverer of Narnia who drove away the Witch and the Winter. All Narnians swear by him."

From "The Horse and His Boy" by C.S. Lewis