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Prepositions after deduce

Deduce from, by, as or in?

Use deduce from to show the evidence or source of a conclusion. Other prepositions usually belong to different sentence structures.

Quick answer

Which preposition follows deduce

The standard pattern is deduce from: We can deduce from the data that sales fell. By may describe the method used to reach a conclusion, but not directly after deduce. As and in are not normal complements after deduce.

Scientists deduced from the evidence that the species migrated early.
We can deduce from her tone that she is upset.
The result was deduced by analysing the samples.

Choose the pattern by meaning

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

1
deduce from + evidence

What information leads to a conclusion

Use from before the facts, signs, or evidence used for reasoning.

The police deduced from the footprints that two people were involved.
Researchers deduced from the survey that remote work was increasing.
2
deduce that + clause

State the conclusion directly

A that-clause can express the conclusion reached.

We deduced that the system had failed during the night.
They deduced that he had left early.
3
by + method with deduce

How the conclusion is reached

By can introduce a method or process connected to the deduction, usually in a longer clause.

The age was estimated by deducing from bone structure how mature the animal was.
She solved the puzzle by deducing from the clues which key was missing.

See the difference in context

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

Construction
Example
Meaning
deduce from
We deduced from the report that costs were rising.
Standard pattern showing the source of the conclusion.
deduce by
The answer was found by deducing from several clues.
By introduces the method, not a direct complement after deduce.
deduce as
They deduced him as the leader.
This is not standard English. Use identify as or deduce that he was the leader.
deduce in
We deduced the pattern in the data.
In here belongs to the noun data, not directly to deduce.

Common mistakes

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

Using as directly after deduce

Deduce does not normally take as.

✕ They deduced him as guilty. ✓ They deduced that he was guilty.

Using in as the complement

In usually belongs to another noun phrase, not to deduce itself.

✕ We deduced in the evidence that he lied. ✓ We deduced from the evidence that he lied.

Using by instead of from for evidence

From introduces the source of the conclusion.

✕ She deduced by the report that sales had fallen. ✓ She deduced from the report that sales had fallen.

Leaving out the source

Deduce often sounds clearer when the evidence is stated.

✓ The detective deduced from the marks that the door had been forced open.

Quick practice

Choose the expression that matches the intended meaning.

1. The scientist deduced ___ the results that the drug was effective.
2. They deduced ___ he had taken the wrong train.
3. She solved the mystery by deducing ___ the clues.

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Frequently asked questions

What is the standard preposition after deduce?

The standard pattern is deduce from, followed by evidence or information.

Can I use deduce by?

By usually introduces a method, as in by deducing from the clues, rather than functioning as the main complement after deduce.

Is deduce as correct?

No. Deduce does not normally take as directly after it.

dabble, in, dabble, with "damage to" or "damage by"? dance to, with, on, in or for? "dangle from" or "dangle in"? dare to, for, on, as or at? dash to, into, out, from or on? daydream about, for, in, of or on? "debate in", "debate on" or "debate with"? deceive by, in, into, on or about? "decide on", "decide to" or "decide by"? declare in, by, on, to or as? decline in, by, from, to or for?

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