What is Constructivism?
Constructivism argues the opposite to objectivism. It is a standpoint that believes social
phenomena are actually constructed by social actors. So, if you had a constructive
ontological worldview you would believe that, for example, a new law is the product of the
behaviour of the group of people it now has an impact on.

What is Positivism?
Positivism generates hypotheses (or research questions) that can be tested and allows
explanations that are measured against accepted knowledge of the world we live in. These
could be the laws of gravity applied to an apple falling from a tree.
This position creates a body of research that can be replicated by other researchers to
generate the same results. The emphasis is on quantifiable results that lend themselves to
statistical analysis.
Links
Wiki about Positivism http://en.wikipedia.org/wiki/Positivism]
Realism
What is Realism?
Realism is similar to positivism in its processes and belief that social reality and the
researcher are independent of each other and so will not create biased results. However,
where they differ is that realism thinks that scientific methods are not perfect. It believes that
all theory can be revised and that our ability to know for certain what reality is may not exist
without continually researching and leaving our minds open to using new methods of
research.
Realism may therefore use several types of research methods to triangulate results in their
search for a more reliable outcome.
Links
Wiki about Critical Realism http://en.wikipedia.org/wiki/Critical_realism