SUFFICIENT CONDITION

Sociologyindex, Sociology Books 2009

In a causal relationship a sufficient condition (or variable) is any variable which is sufficient to bring about the effect in question.

For example, a growing unemployment rate might be sufficient to cause an increase in the crime rate. Obviously many other factors (variables) could also cause the increase.

Typically there are many conditions sufficient to cause an increase, or a decrease, in crime.

From: sfu.ca/philosophy/swartz/conditions1.htm - Definition: A condition A is said to be sufficient for a condition B, if (and only if) the truth (/existence /occurrence) [as the case may be] of A guarantees (or brings about) the truth (/existence /occurrence) of B.

For example, while air is a necessary condition for human life, it is by no means a sufficient condition, i.e. it does not, by itself, i.e. alone, suffice for human life. While someone may have air to breathe, that person will still die if s/he lacks water (for a number of days), has taken poison, is exposed to extremes of cold or heat, etc. There are, in fact, a very great many conditions that are necessary for human life, and no one - or even just a few of them - will suffice for [or guarantee] human life. Or, further, consider the property of having four sides. While having four sides is a necessary condition for something's being a square, that single condition is not, by itself, sufficient (to guarantee) something's being a square, i.e. some four-sided things (e.g. trapezoids) are not squares. There are several necessary conditions for something's being a square, and all of these must be satisfied for something's being a square: 
x has (exactly) four sides
each of x's sides is straight
x is a closed figure
x lies in a plane
each of x's sides is equal in length to each of the others
each of x's interior angles is equal to the others (they are each right [i.e. 90o] angles) 
the sides of x are joined at their ends 
The foregoing is a complete set of necessary conditions, i.e. the set comprises a set of sufficient condition for x's being square. 
Frequently the terminology of "individually necessary" and "jointly sufficient" is used. One might say, for example, "each of the members of the foregoing set is individually necessary and, taken all together, they are jointly sufficient for x's being a square." 
Caution: In this example, we have been able, with ease, to list a set of individually necessary conditions that is also sufficient for something's being a square. However, we must not generalize from this simple example and believe that it is usually, or often, a straightforward task to specify sets of conditions that are individually necessary and jointly sufficient. Sometimes it is much easier to specify (some, or many, of the) necessary conditions even though we are unable to specify a set that is jointly sufficient. Other times, the converse is true: for some cases it will be easier to specify sufficient conditions without our being able to specify individually necessary ones. - sfu.ca/philosophy/swartz/conditions1.htm