Perimeter & Parameter

Perimeter (pronounced puh-rim-i-ter)

(1) A line bounding or marking off an area; any boundary around.

(2) The outermost limits.

(3) In geometry, the border or outer boundary of a two-dimensional figure (the sum of the lengths of the segments that form the sides of a polygon.

(4) The total length of such line; the total length of any such closed curve, such as the circumference of a circle.

(5) In military jargon a fortified boundary that protects a position.

(6) In clinical ophthalmology, an instrument for determining the peripheral field of vision.

(7) In basketball, a semicircular line on a basketball court surrounding the basket, outside of which field goals are worth three points rather than two (also called three-point line).

(8) The area outside this line (often used attributively).

1585–1595: From the French périmètre (circumference, outer boundary, or border of a figure or surface), from the feminine Latin form perimetros, from the neuter Greek perímetron (circumference), the construct being peri- (around; about) + -meter from metron (measure), from the primitive Indo-European root me- (to measure).  The military sense of “boundary of a defended position” is said by some sources to have come into use only by 1943 despite the tactic being probably the second oldest military procedure still in use (the attack presumably the first).  Whether coincidental or not, the ultimate failure of perimeter defense was what finally led to the success of the Soviet offensive against the Nazi Sixth Army in Stalingrad (now Volgagrad) in 1943.  The technical terms created by the use of perimeter as a modifier include perimeter check (a patrol which checks to ensure a defensive perimeter remains in place) & perimeter fence.  Perimeter & perimetry are nouns, perimetral, perimetric & perimetrical are adjectives and perimetrically is an adverb; the noun plural is perimeters.

Parameter (pronounced puh-ram-uh-tuhr (U) or puh-ram-i-ter (non-U)

(1) In mathematics, a constant or variable term in a function that determines the specific form of the function but not its general nature, as a in f(x) = ax, where a determines only the slope of the line described by f(x).  (A value kept constant during an experiment, equation, calculation or similar, but varied over other versions of the experiment, equation, calculation etc).

(2) In mathematics, one of the independent variables in a set of parametric equations.

(3) In geometry, in the ellipse and hyperbola, a third proportional to any diameter and its conjugate, or in the parabola, to any abscissa and the corresponding ordinate.

(4) In crystallography, the ratio of the three crystallographic axes which determines the position of any plane; the fundamental axial ratio for a given species.

(5) In statistics, a variable entering into the mathematical form of any distribution such that the possible values of the variable correspond to different distributions (any measured quantity of a statistical population that summarizes or describes an aspect of the population).

(6) In computing, a variable that must be given a specific value during the execution of a program or of a procedure within a program.

(7) Limits or boundaries; guidelines; specifications; any constant, definitional or limiting factor (usually in the plural parameters).

(8) Characteristic or a factor; an aspect or element.

(9) In computing syntax for various purposes, an input variable of a function definition, that become an actual value (argument) at execution time (an actual value given to such a formal parameter).

1650-1660: From the French paramètre, from the New Latin parametrum (parameter), the construct being the Ancient Greek παρα- (para-) (beside, subsidiary) + μέτρον (métron) (meter) (measure), from the primitive Indo-European root me- (to measure).  The words was almost exclusive to mathematics & geometry until the late 1920s when it came to be extended to “measurable factor(s) which help to define a particular system", hence the now common alternative meaning “boundary, limit, characteristic factor” (under the influence of perimeter which used a similar spelling and (at least conceptually) could be understood to enjoy some overlap of meaning.  Although the wider definition has been in use since the 1950s, purists have never approved.  Parameter is a noun and parametric & parametrical are adjectives; the noun plural is parameters.

Parameters and perimeters

The more modern ways “parameter” has been used since the early twentieth century does offend the linguistically more fastidious but it seems clear the innovations are here to stay.  Some do however just get it wrong and university lecturers in the social sciences seem to be those who bear the heaviest burden of training a certain number of their institution’s first year students in the correct use of “parameter” & “perimeter”.  That they are sometimes confused is understandable because the spellings are so close and there is some sense of overlap in the meanings, both able to be used in a way which defines limits.  The definitions can be reduced to: (1) perimeter refers to either something physical (a national border; a fence etc) or a representation of something physical (lines on a map; the four sides of a square etc) whereas (2) a parameter is an element of specification, a constant or variable value which can be either an absolute value or a range.  So, a perimeter may be drawn on the basis of certain parameters while the values of parameters will in some cases exist within certain perimeters.  Definitions such as that are vague enough for those so inclined to find contradictions but for the way most people, most of the time (correctly) use parameter & perimeter, it seems serviceable.

Lindsay Lohan and her lawyer in court, Los Angeles, December 2011.