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Instrumental rationality is a mode of thought and action that identifies problems and works directly towards their solution.
Instrumental rationality is often studied as a social phenomenon by sociology, social philosophy and critical theory. Perhaps its most famous critic is philosopher Martin Heidegger, who argued that the greatest danger facing modern humans was their own instrumental relationship to the world.
Definition and disciplines 
Instrumental rationality is often seen as a specific form of rationality focusing on the most efficient or cost-effective means to achieve a specific end, but not in itself reflecting on the value of that end. Thus, to the extent that rationality is concerned with critically evaluating actions, instrumental rationality tends to focus on the 'hows' of an action, rather than its 'whys'.
More specifically, instrumental rationality can be contrasted with forms of rationality concerned with (a) promoting human understanding on a more general level, or (b) with improving the human condition. Thus, Jürgen Habermas, in his early philosophy of science (such as his book Technik und Wissenschaft als „Ideologie“ from 1968), distinguished between three different forms of "knowledge interests" (Erkenntnisinteressen) that were constitutive of three forms of the scientific enterprise, namely (a) the interest in understanding, constitutive of the humanities; (b) the interest in critical questioning forms of oppression, ideally constitutive of social sciences, and finally, (c) the interest in understanding the necessities of nature and the potential for technically harnessing natural laws, and manipulating living and dead nature, constitutive of the natural sciences. The latter is an expression of instrumental rationality.
However, to a large extent, the social sciences, such as economics, are also investigating how the laws of economy constrain human action and how to manipulate those laws or conditions. Thus, we find in economics many expressions of instrumental rationality. Instrumentally rational agents take the course of action that will optimally achieve their desired ends in any situation, the choice of ends being given. It is distinguished from philosophies that propose to use reason to prescribe the ultimate goals. Instrumental rationality uses reason only as a tool to reach the goals, not to say which goals are right.
Varieties of instrumental rationality include descriptive instrumental rationality (DIR), which says agents behave as instrumental rationalists as a matter of fact; descriptive selfish instrumental rationality, which extends DIR to say that agents pursue selfish ends (e.g., financial gain, pleasure); and prescriptive instrumental rationality, which claims agents ought to pursue their ends as instrumental rationalists.
Proponents of instrumental reason counter that reason in and of itself cannot reach a conclusion on ultimate goals, using arguments of the type originated by David Hume, and that those who say it can are attempting to force a political decision by a more elaborate form of begging the question. The position is called moral nihilism and can lead to amoralism, if nonrational reasons for ultimate goals are dismissed.
Historically, French philosophy from the eighteenth century has generally been opposed to this concept while British philosophy has often accepted it.
Instrumental rationality became a major theme of Continental philosophy in the 19th and 20th centuries.
In a short but influential essay titled "The Question Concerning Technology", Martin Heidegger defined the instrumental attitude as a threat to the world and to the human spirit:
The essence of technology lies in Enframing. Its holding sway belongs within destining. Since destining at any given time starts man on a way of revealing, man, thus under way, is continually approaching the brink of the possibility of pursuing and pushing forward nothing but what is revealed in ordering, and of deriving all his standards on this basis. Through this the other possibility is blocked, that man might be admitted more and sooner and ever more primally to the essence of that which is unconcealed and to its unconcealment, in order that he might experience as his essence his needed belonging to revealing.
Yet when destining reigns in the mode of Enframing, it is the supreme danger. This danger attests itself to us in two ways. As soon as what is unconcealed no longer concerns man even as object, but does so, rather, exclusively as standing-reserve, and man in the midst of objectlessness is nothing but the orderer of the standing-reserve, then he comes to the very brink of a precipitous fall; that is, he comes to the point where he himself will have to be taken as standing-reserve. Meanwhile man, precisely as the one so threatened, exalts himself to the posture of lord of the earth. In this way the impression comes to prevail that everything man encounters exists only insofar as it is his construct. This illusion gives rise in turn to one final delusion: It seems as though man everywhere and always encounters only himself.
Max Horkheimer and other members of the Frankfurt school made similar criticism, adding a Marxist dimension to their analysis. In “On the Critique of Instrumental Reason” and "Means and Ends", Horkheimer argues that instrumental rationality plays a key role in the oppressive industrial culture of capitalism.
Measuring instruments 
Instrumental rationality can also refer to physical instruments and the processes of measurement and control. An ammeter, for example, combines the physical phenomena of electromagnetism with the geometric rationality of trigonometry. In this tradition, "instrumental rationality" is often simply called "instrumentation".
See also 
- Rationality and power
- Rationalisation (social process)
- Social action
- Instrumental action
- Homo economicus
- Heidegger, Martin (1950). "The Question Concerning Technology".
- Zalta, Edward N. (24 June 2009). "Max Horkheimer". Stanford Encyclopedia of Philosophy. Retrieved 27 August 2012.