# Left and right

A right-handed Cartesian coordinate system, presenting the z (up) vector and y (forward) vector, the right is defined to be the positive x vector. In this image, left and right are defined from the attacking boxer's perspective.

Left, right, forward, and back are the relative directions. They change as a person moves. People are often confused by the relative nature of these directions. "Left" for one person is different from "left" for another. Unlike the cardinal directions (North, South, East, and West), left and right are based solely on the viewer's perspective.

The terms are derived from the fact that some 90% of the population are right-handed, that is, favour their right hand for a variety of tasks. The direction right is a cognate of "right" meaning correct or good. The word "left" comes from the Old English lyft, meaning weak. This dichotomy can also be seen in the words "dextrous" and "sinister", from the Latin words for right and left.

In the vast majority of the population, the heart is slightly to the left of the body's centre line and the liver is to the right. Less visibly, the two hemispheres of the brain differ in function.

Mirrors are said to reverse left and right. Strictly, this is not true: the image of one's left hand is on his or her left-hand side. However, it is seen at the position corresponding to that of the right hand of a real person opposite to him or her. Thus one can say that the mirror has the combined effect of turning you around and reversing left and right. One can also say that it reverses front and back side. If one takes a cube and writes "left", "right", "top", "bottom", "front", and "back" and holds it so that all sides face the correct direction, then hold a mirror behind it, without moving the cube or himself or herself, one will notice that "front" and "back" are swapped in the mirror image, but the other sides are still correctly labelled.

In nautical usage, the halves of a ship are designated port (left) and starboard (right), relative to a person looking forward (towards the bow of the ship).

In politics, "left" and "right" are labels applied to socialist and conservative political figures or ideologies, respectively. The terms derive from the seating of parliamentary partisans during the French Revolution; see left-wing politics and right-wing politics.

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