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Prepositions after verbs

Swear by or swear to?

Swear by means strongly believe in or rely on something. Swear to means formally declare or promise something as true.

Quick answer

What is the difference between swear by and swear to?

Use swear by for strong trust or approval. Use swear to for legal statements, promises, or confirming facts.

She swears by herbal remedies.
The witness swore to tell the truth.
Many runners swear by this training method.
He swore to the accuracy of the report.

Choose the pattern by meaning

These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.

1
swear by + thing/method

Showing strong belief or reliance

Use swear by when someone strongly trusts or recommends something.

My grandmother swears by this soup recipe.
Athletes swear by regular stretching.
2
swear to + statement/promise

Making a formal declaration

Use swear to for legal, official, or serious statements.

She swore to keep the information secret.
The officer swore to the contents of the document.
3
swear at + person

Using angry language

Swear at has a different meaning: to use rude language toward someone.

He swore at the driver.
The customer swore at the staff member.

See the difference in context

The same subject can take different constructions because each sentence answers a different question.

Construction
Example
Meaning
swear by
I swear by this software.
strongly trust or recommend
swear to
She swore to tell the truth.
formally promise or confirm
swear at
He swore at the referee.
use offensive language toward someone
swear on
They swore on the Bible.
make an oath using a sacred object

Common mistakes

Some combinations appear in real text but do not mean what learners often assume.

Using swear by for legal promises

Formal declarations usually take to.

✕ He swore by tell the truth. ✓ He swore to tell the truth.

Using swear to for preferences

Use by when talking about trust in a product or method.

✕ She swears to this skincare routine. ✓ She swears by this skincare routine.

Confusing swear at with swear to

Swear at means use rude language toward someone.

✕ He swore to the waiter during the argument. ✓ He swore at the waiter during the argument.

Quick practice

Choose the expression that matches the intended meaning.

1. Many chefs swear ___ cast-iron pans.
2. The witness swore ___ tell the truth.
3. He was angry and swore ___ the taxi driver.

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Frequently asked questions

Can swear by mean recommend?

Yes. People often use swear by for products, routines, or methods they strongly trust.

Is swear to only legal?

No. It can also be used for serious promises outside legal settings.

What does swear on mean?

Swear on refers to making an oath using something important or sacred, such as swear on a holy book.

sack, by, sack, for, sack, from "sacrifice for" or "sacrifice to"? sail from, in, for, to or through? "salvage from" or "salvage in"? sanction by, for, in, with or according? satisfy with, by, in, about or after? "saturate with" or "saturate in"? save by, for, from, on or in? "say in", "say about" or "say to"? "scan for", "scan in" or "scan through"? "scar by" or "scar on"? scatter in, across, around, throughout or on?

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