The circumflex often changes the sound of the vowel it's over, making pronunciation distinct. The 'â' in 'pâte' sounds different from the 'a' in 'patte'.
Pro Tip 2/3
Historical Letters
In some languages, the circumflex indicates a historical letter that no longer exists. French 'hôpital' used to be spelled 'hospital', the circumflex replaced 's'.
Pro Tip 3/3
Spelling Conventions
It's crucial to memorize circumflex use in vocabulary as it may affect meaning. 'Du' and 'dû' in French have different meanings.