By-Phrases

Fixed expressions with 'by': by mistake, by accident, by chance, by heart, by hand. These phrases express manner or means and must be memorised as units.

By-Phrases in English

'By' in fixed idiomatic phrases expresses the manner or means by which something happens. These phrases cannot be derived from grammar rules — each one is a lexical unit that must be memorised. Corpus data from the British National Corpus shows that 'by mistake', 'by chance', and 'by heart' are among the 500 most frequent prepositional phrase collocations in English, making them essential vocabulary at B1 level.

Core By-Phrases

by mistake — I called the wrong number by mistake.
by accident — She found the letter by accident while tidying up.
by chance — We met by chance at the airport.
by heart — He knows the whole poem by heart.
by hand — This bag was sewn by hand.

By Mistake vs On Purpose

'By mistake' and 'by accident' describe unintentional actions. Their direct opposite is 'on purpose' (intentional). Russian speakers often produce 'on mistake' because the Russian «по ошибке» maps onto 'on' — but English requires 'by'.

Common Mistakes

✗ She broke the window on mistake. → ✓ She broke the window by mistake.
✗ I learned this song on heart. → ✓ I learned this song by heart.
✗ We met with chance. → ✓ We met by chance.