All of a sudden
'All of a sudden' sounds like the kind of poetic version of 'suddenly' that would do justice to Shakespeare. In fact, that's what Shakespeare thought too, as it was he who coined the phrase. In The Taming of the Shrew, circa 1596, we find:
Is it possible That love should of a sodaine take such hold?
[Note: 'sodaine' was one of the numerous Tudor spellings of 'sudden'.]
With that coinage, Shakespeare gave us the version of the expression that most grammarians now prefer. The modern alternative 'all of the sudden', which is preferred by the young, is disparaged as non-standard English. In fact, there's no good grammatical reason to say 'all of a sudden' in preference to 'all of the sudden'. If we go back beyond Shakespeare the variant 'the sudden' was commonplace; for example, in John Greenwood's Collection of Articles [of Henry Barrow and others], 1590, we find:
I was compelled to answere of the sodaine vnto such articles.
See other phrases and sayings from Shakespeare.