A little knowledge is a dangerous thing
A small amount of knowledge can mislead people into thinking that they are more expert than they really are.
'A little knowledge is a dangerous thing' and 'a little learning is a dangerous thing' have been used synonymously since the 18th century.
The version 'a little learning' is widely attributed to Alexander Pope (1688 - 1744). It is found in An Essay on Criticism, 1709, and I can find no earlier example of the expression in print:
A little learning is a dangerous thing;
drink deep, or taste not the Pierian spring:
there shallow draughts intoxicate the brain,
and drinking largely sobers us again.
The similarity of the two phrases is demonstrated by what appears to be an impromptu coining of 'a little knowledge is a dangerous thing' in a piece in The monthly miscellany; or Gentleman and Lady's Complete Magazine, Vol II, 1774, in which the writer misquoted Pope:
Mr. Pope says, very truly, "A little knowledge is a dangerous thing."
Both Pope's original verse and the misquotation of it were predated by an anonymous author, signing himself 'A B', in the collection of letters published in 1698 as The mystery of phanaticism:
"Twas well observed by my Lord Bacon, That a little knowledge is apt to puff up, and make men giddy, but a greater share of it will set them right, and bring them to low and humble thoughts of themselves.
Again, there is a degree of misquotation here; what 'my Lord Bacon', the English politician and philosopher Francis Bacon, Viscount St Alban, actually said, in The Essays: Of Atheism, 1601, was:
"A little philosophy inclineth man’s mind to atheism; but depth in philosophy bringeth men’s minds about to religion."
So, who coined the phrase? It appears to have been a group effort. Bacon can be credited with the idea, Pope with the 'learning' version and the mysterious 'A B' with the 'knowledge' version.
See also: the List of Proverbs.
See also: the last words of Sir Francis Bacon.