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Prepositions after verbs

Alter by or alter in?

Alter by and alter in are both possible, but they express different ideas. By refers to the amount of change. In refers to the area or aspect where the change happens.

Quick answer

Use by for degree and in for area

Alter by introduces the amount or measure of change. Alter in introduces the field, feature, or area affected by the change.

Prices were altered by 10 percent.
The design was altered in several places.
Her voice altered in tone after the announcement.

Choose the pattern by meaning

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

1
alter by + amount

How much does something change?

Use by with numbers, percentages, or measures of difference.

The schedule was altered by two days.
2
alter in + aspect

In what way does something change?

Use in with qualities, areas, or features.

The policy was altered in minor details.
3
alter something to + new form

What new form results?

Alter to introduces the resulting state or form.

They altered the room to a modern style.
4
alter with + tool/substance

What causes the change?

With may introduce the means or material used to alter something.

The image was altered with editing software.

See the difference in context

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

Construction
Example
Meaning
alter by
Production costs altered by 5 percent.
Shows the degree or amount of change.
alter in
The document was altered in several sections.
Shows the area or aspect affected.
alter to
They altered the plan to fit the budget.
Shows the new form or purpose after change.

Common mistakes

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

Using by for the area of change

By usually expresses amount, not location or aspect.

✕ The report was altered by several sections. ✓ The report was altered in several sections.

Using in with numbers

Use by for amounts or percentages.

✕ Sales altered in 15 percent. ✓ Sales altered by 15 percent.

Confusing alter and alternate

Alter means change. Alternate means switch back and forth.

✕ The lights altered between red and green. ✓ The lights alternated between red and green.

Quick practice

Choose the expression that matches the intended meaning.

1. The deadline was altered ___ three days.
2. The agreement was altered ___ a few details.
3. The editor altered the image ___ professional software.

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Frequently asked questions

Can alter by and alter in both be correct?

Yes, but they have different meanings. By shows amount, while in shows the area affected.

Is alter to also possible?

Yes. Alter to can introduce the new form or purpose.

What is the difference between alter and change?

Alter often suggests partial modification, while change can describe any kind of difference.

abandon, by, abandon, in "abduct by", "abduct in" or "abduct from"? abide by, in, with, to or on? "abolish in" or "abolish by"? "abound in" or "abound with"? "absorb by", "absorb into" or "absorb in"? "accelerate by", "accelerate to" or "accelerate in"? accentuate by, with, in or under? accept by, in, as, for or into? "accommodate in", "accommodate for" or "accommodate to"? "accomplish by" or "accomplish in"? "accord to" or "accord with"?

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