# fathom out

CEFR C1 · Phrasal verb

Source: https://englishreference.com/word/fathom-out
Updated: 2026-04-24

## Definition

to finally understand something that is very difficult or mysterious after thinking about it for a long time.

For teachers: to discern or comprehend a complex problem or mysterious situation through careful thought; often used in the negative to express total confusion.

## Examples

- I can't fathom out why he decided to quit his job.
- It took the detectives several weeks to fathom out how the thief had entered the building without triggering the alarm.
- Historians are still attempting to fathom out the exact sequence of events that led to the sudden collapse of the ancient civilization.

## Pitfalls

- Not "I couldn't fathom out it." but "I couldn't fathom it out." — when using a pronoun like 'it', it must go between the verb and the particle because this phrasal verb is optional in its separability.

## Usage notes

- chiefly British English; the object can be a noun phrase or a 'wh-' clause.
- Teaching tip: anchor this to the noun 'fathom' (a unit of water depth) to help students visualize 'getting to the bottom' of a deep or murky problem.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.