What does knee-jerk reaction mean?

From NYT article:

Another senior Socialist, who declined to be identified, said the party could not afford knee-jerk reactions.

  • 1
    Have you ever had a doctor tap your knee with that funny-looking little hammer?
    – Hot Licks
    Jul 26 '16 at 19:58

A knee-jerk reaction indicates a reflexive response.

There are a couple of particular concerns with such responses:

  • They're spontaneous and generally involuntary
  • Haste being necessarily so, these can often be detrimental to a situation, with no forethought as to the consequences

These are benefits in nature (if falling, notice that arms automatically attempt break the fall, particularly protecting the head); when applied to speech and whatnot, such as in office, it isn't a recommended practice to work solely from 'instincts' (for example, if a suggestion strikes a nerve with one member, emotions may speak for him, as opposed to taking an objective standpoint.)


It's an expression/saying meaning:

An immediate unthinking emotional reaction produced by an event or statement to which the reacting person is highly sensitive;

It's origin is thus:

From the tendency of the knee to jerk involuntarily when hit sharply, properly called the patellar reflex. That was recorded by Sir Michael Foster in his Text-book of physiology, 1877:

"Striking the tendon below the patella gives rise to a sudden extension of the leg, known as the knee-jerk."

The term began to be used figuratively from the early 20th century onwards. O. O. McIntyre, in his New York Day-By-Day column in The Coshocton Tribune, October 1921, wrote this:

"Itinerant preacher stemming Broadway on a soap box. And gets only an occasional knee-jerk."



  • 1
    +1 for mentioning that it derives from the patellar reflex (video).
    – psmears
    Jul 1 '11 at 14:01
  • Patellar reflex or when the doctor taps your knee with the hammer is not the same as knee jerk reaction which is an involuntary psychologically generated bodily reaction. It happens when someone says something contradicting or challenging to a strongly held opinion you have and you get this involuntary knee jerk. Aug 18 '18 at 13:16
  • It's a "metaphor"
    – user184130
    Aug 18 '18 at 13:24

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