Here is an excerpt of a great little book called "On Bullshit" by Harry Frankfurt. The full text can be viewed here.

One of the most salient features of our culture is that there is so much bullshit. Everyone knows this. Each of us contributes his share. But we tend to take the situation for granted. Most people are rather confident of their ability to recognize bullshit and to avoid being taken in by it. So the phenomenon has not aroused much deliberate concern, or attracted much sustained inquiry. In consequence, we have no clear understanding of what bullshit is, why there is so much of it, or what functions it serves. And we lack a conscientiously developed appreciation of what it means to us. In other words, we have no theory. I propose to begin the development of a theoretical understanding of bullshit, mainly by providing some tentative and exploratory philosophical analysis. I shall not consider the rhetorical uses and misuses of bullshit. My aim is simply to give a rough account of what bullshit is and how it differs from what it is not, or (putting it somewhat differently) to articulate, more or less sketchily, the structure of its concept.

The essay goes on to dissect much of modern discourse, showing how subjectivity and manipulation allow people to deceive even themselves. A lot of this has come from the postmodern embrace of relativism and constructivism. Perception (deception) in many quarters has become reality.

The contemporary proliferation of bullshit also has deeper sources, in various forms of skepticism which deny that we can have any reliable access to an objective reality and which therefore reject the possibility of knowing how things truly are. These “anti-realist” doctrines undermine confidence in the value of disinterested efforts to determine what is true and what is false, and even in the intelligibility of the notion of objective inquiry. One response to this loss of confidence has been a retreat from the discipline required by dedication to the ideal of correctness to a quite different sort of discipline, which is imposed by pursuit of an alternative ideal of sincerity. Rather than seeking primarily to arrive at accurate representations of a common world, the individual turns toward trying to provide honest representations of himself. Convinced that reality has no inherent nature, which he might hope to identify as the truth about things, he devotes himself to being true to his own nature. It is as though he decides that since it makes no sense to try to be true to the facts, he must therefore try instead to be true to himself.

The essay concludes with the following statement:

But it is preposterous to imagine that we ourselves are determinate, and hence susceptible both to correct and to incorrect descriptions, while supposing that the ascription of determinacy to anything else has been exposed as a mistake. As conscious beings, we exist only in response to other things, and we cannot know ourselves at all without knowing them. Moreover, there is nothing in theory, and certainly nothing in experience, to support the extraordinary judgment that it is the truth about himself that is the easiest for a person to know. Facts about ourselves are not peculiarly solid and resistant to skeptical dissolution. Our natures are, indeed, elusively insubstantial — notoriously less stable and less inherent than the natures of other things. And insofar as this is the case, sincerity itself is bullshit.