Social constructionism

In postmodern philosophy, social constructionism is the position that knowledge, including knowledge of reality, is socially constructed; in its extreme form, that there is no such thing as objective reality to know about (or that objective reality is philosophically unknowable), only social constructs which are labeled "knowledge of reality." Science will carry some human construction because it's a human endeavor, and it's important to be mindful of this.

A brief illustration
There is often much to-do about whether something is "real" or if it is "merely" a social construct. An old joke is often brought up at this point: "If you believe social constructions aren't real, then please take out all the bills in your wallet and pass them up to me." Money is, indeed, a classic example of a social construction that plays an extremely important role in our everyday lives. All those paper bills and coins are "just" paper and metal, and all that money in your bank account is "just" some numbers in a computer. Think about that for a moment — or don't, you might ruin the economy.

Strong vs. weak social constructionism
There are two general strains of social constructionism: strong and weak. The strong form denies an important distinction made by the weak form. In The Construction of Social Reality (1995), John Searle, borrowing the concept from G.E.M. Anscombe, distinguishes between "brute facts" and "institutional facts". Brute facts do not rely on any more fundamental facts. Institutional facts, however, are the product of social conventions.

The strong version of social constructionism rejects the above distinction and posits that all knowledge is socially constructed through action and speech. This position is easily refuted in a number of ways. While it may be difficult in some cases to draw a clear distinction between brute and institutional facts, one can argue (as Searle does) that there are clear instances of fact that do not rely on social convention — such as the eruption of a volcano. Another line of argumentation is to accept the basic premises of the strong version but to argue that the consequences are either trivial or incoherent.

Many objections to science come from excesses of social constructionism. For example, scientific racism has generated lots of studies that just happen to have concurred with whatever popular prejudice was at the time of writing. While the extreme social-constructionist position is ridiculous (though it exists, for example, in much of New Age thought), scientists are human and therefore full of shit, and the science they come up with can, if unchecked, carry ridiculous amounts of entirely local cultural baggage. In the course of time, sciences tend to get less constructed and more objective; the really successful scientific models, like evolution or quantum mechanics, are truly alien to common human thinking and may transcend cultural boundaries (but also find strong resistance from cultural constructs such as creationism or relativity denial).