What is theoretical postmodernism?

Postmodernism, as a framework, is a way of challenging or re-assessing the theories and ways of thinking developed in the modern context. It deals heavily with skepticism and epistemology--how do we know what we know? Theoretical postmodernism emphasizes relativity in developing theory, and is used widely in the social sciences as a means of addressing the subjective nature of knowledge and truth.

Someone who works with postmodernist thought should be no stranger to the fact...

Postmodernism, as a framework, is a way of challenging or re-assessing the theories and ways of thinking developed in the modern context. It deals heavily with skepticism and epistemology--how do we know what we know? Theoretical postmodernism emphasizes relativity in developing theory, and is used widely in the social sciences as a means of addressing the subjective nature of knowledge and truth.

Someone who works with postmodernist thought should be no stranger to the fact that knowledge changes over time. Modernist philosophy emphasizes the use of logic and reason and asserts that there is a concrete, quantifiable, and even predictable or certain nature to the world. While a modernist might feel that the world can be easily understood and explained through theory developed through methodical, logical reasoning, a postmodernist recognizes the importance of subjectivity. 

To put it in a very abstract example, a modernist might measure a sack of potatoes using standardized weights and determine that it weighs one kilo. The postmodernist acknowledges that the weight of the sack of potatoes is determined by a previously established and arbitrary system of measurement.