"My aim is: to teach you to pass from a piece of disguised nonsense to something that is patent nonsense." (Part I, section 464)
Traditional philosophy, according to Wittgenstein, is made up of "disguised nonsense." He believes that philosophers debate theories that seem plausible when set forward in a philosophical context. However, the very formulation of these theories is founded on unwarranted assumptions and generalizations that we fail to notice because they take place at such a fundamental level. Philosophical Investigations does not attack these sorts of theories head on, but rather probes the fundamental assumptions and generalizations that motivate them. At such a fundamental stage, the error is far more evident, and so far easier to expose. At this level we are dealing with "patent" nonsense. The purpose of the Investigations is to show that this patent nonsense is the very stuff that makes philosophical theories seem plausible.