He knows not a hawk from a hand-saw.

Understand the thought

Meaning in plain English

The phrase mocks someone for failing to recognise an obvious difference. Use its meaning to understand the criticism, while avoiding a sweeping judgement about a person from one gap in their knowledge.

What the words are saying

The hawk and hand-saw are presented as things the person cannot distinguish. In this short source wording, the force is an accusation of poor recognition or judgement, rather than an explained factual account. No origin, earlier spelling or literary attribution is claimed here. A modern use may be exaggerated: someone unfamiliar with one subject can still be capable elsewhere. The useful question is which particular distinction matters and whether a clearer explanation would help. Interpreting the phrase does not require endorsing the mockery or assuming that everyone has had the same opportunity to learn what seems obvious to the speaker.

Everyday example

Instead of mocking a new volunteer for confusing two catalogue labels, an experienced colleague explains the distinction needed for that particular task.

When to use it

Use it mainly to recognise an exaggerated criticism of someone’s ability to distinguish things.

Agent-assisted editorial interpretation. This explains the words; it does not by itself verify their author or earliest origin.