Posted by Long John on May 06, 2001
In Reply to: Don't buy a pig in a poke; an explanation posted by James Briggs on November 07, 2000
: : do not buy anything 'sight unseen'
: Yes, but what's its origin? This goes with another, similar saying.
: To let the cat out of the bag is said to occur if a secret is revealed. In medieval times piglets were often taken to market in a sack where they were sold. If the purchaser was particularly gullible he was sometimes sold not a piglet, but a cat in the sack. Cats are versatile animals and sometimes managed to escape - the cat was truly out of the bag. In similar manner it was possible to be sold a pup. Incidentally, the sack or bag was correctly termed a poke, hence a pig in a poke. To be sold a pig in a poke was clearly the object of the exercise and why it has come to imply a swindle I can't understand. However, there are other sayings and words which have reversed their meanings over the years. Why this should be so is not understood but this drift of meaning is known as catachresis. A good example of drift is found in the word Brave. In the past it implied cowardice as, indeed, Bravado still does. Incidentally, the diminutive of poke lives on today in modern English in the form of Pocket.
The phrase implies a swindle because it should be interpreted as an instruction, ie if you buy a pig do not buy it in a poke (as if you do it may not be a pig after all).