by sight

by sight — idiom

1. able to recognize a person because you have seen them before, even though you ha

1.idiomB2
Definition

able to recognize a person because you have seen them before, even though you have never spoken to them or learned their name.

Example

Eve knew the old postman by sight, but they had never once spoken.

know someone by sight (recognize without knowing personally)

Most students knew the head teacher only by sight, not as a friend.

know only by sight (recognition without acquaintance)

Common collocations
  • know by sight
  • recognize by sight
  • only by sight
Synonyms
  • by appearance

    plainer; stresses physical looks rather than the act of recognizing

Antonyms
  • by name

    knowing who someone is well enough to call them by name

Grammar Patterns

know someone by sight

Usage Note

Almost always used with 'know' or 'recognize'. It marks recognition by appearance only, so it is naturally contrasted with knowing someone personally or by name.

Common Mistakes

I know him by sight personally.
I know him by sight, but not personally.
'by sight' means you recognize the face only, so it cannot be paired with 'personally'.

Etymology

Old EnglishEnglish

Built from the preposition 'by', here meaning 'by means of', and the noun 'sight', the act of seeing. The phrase has been used since the 1500s to describe recognizing someone purely through having seen them, as opposed to knowing them in person.