we need to differentiate between philosophical realism and scientific realism
philosophical Realism : Contemporary philosophical realism is the belief that our reality, or some aspect of it, is ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc. Realism may be spoken of with respect to other minds, the past, the future, universals, mathematical entities (such as natural numbers), moral categories, the material world, and thought. Realism can also be promoted in an unqualified sense, in which case it asserts the mind-independent existence of a visible world, as opposed to idealism, skepticism, and solipsism. Philosophers who profess realism state that truth consists in the mind's correspondence to reality (from
http://en.wikipedia.org/wiki/Philosophical_realism)
This is in opposite to idealism.It should be noted that one can be realist about certain things(say material world) and anti-realist about others(mathematical entities,moral truths). so when discussing realism before proceeding further we need to clear about which entities we are talking.
Scientific realism : It is a particular form of philosophical realism. Scientific realism is, at the most general level, the view that the world described by science (perhaps ideal science) is the real world, as it is, independent of what we might take it to be. Within philosophy of science, it is often framed as an answer to the question "how is the success of science to be explained?" The debate over what the success of science involves centers primarily on the status of unobservable entities apparently talked about by scientific theories. Generally, those who are scientific realists assert that one can make reliable claims about unobservables (viz., that they have the same ontological status) as observables, as opposed to instrumentalism. (from
http://en.wikipedia.org/wiki/Scientific_realism) .
The debate between scientific realism and antirealism arises when we consider the question what does the best confirmed theories tell about the external world.
The basic argument for scientific realism consists of 3 premises
The claims the theory makes are either true or false, depending on whether the entities talked about by the theory exist and are correctly described by the theory. This is the
semantic commitment of scientific realism.
The entities described by the scientific theory exist objectively and mind-independently. This is the
metaphysical commitment of scientific realism.
There are reasons to believe some significant portion of what the theory says. This is the
epistemological commitment.
IA scientific anti-realist rejects any one or more of the above premises. One can be metaphysical realist and still be scientific anti-realist because you can reject any other two premises(semantic/epistemological). In fact most of scientific anti-realist are metaphysical realists.The current debate between scientific realism/anti-realism is mainly regarding UN-observable entities like electron etc. (see this short video
http://www.youtube.com/watch?v=eDUciNH-gIE on philosophy of science). Instrumentalism is a prominent form of scientific anti-realism it is the view that a scientific theory is a useful instrument in understanding the world. A concept or theory should be evaluated by how effectively it explains and predicts phenomena, as opposed to how accurately it describes objective reality.( see
http://en.wikipedia.org/wiki/Instrumentalism)
scientists can be both realists (like Einstein) or instrumentalists (like Feynman and other 'shut up and calculate' school of quantum mechanics. science doesn't explicit make metaphysical claims. it is the jobof philosophers of science to explain the metaphysical implications of science
There is a new position called structural realism which tries to combine both of them. see
http://rationallyspeaking.blogspot.in/20...ysics.html and
http://plato.stanford.edu/entries/structural-realism/
For a detailed study of the topic see the book Understanding philosophy of science by James Ladyman ch 5 to 8