Passage Summary: Because people see a huge number of commercials by middle age, those commercials must be changing how people think.

Conclusion: Television commercials have had an impact on the way North Americans think.

Reasoning: By the age of 40, the average person in North America has been exposed to over a million TV advertisements.

Analysis: There is a clear gap between the sheer volume of exposure (the premise) and the actual effect on internal thought processes (the conclusion). Just because you see something a million times doesn't guarantee it changes your mind; you might just ignore it. To make this argument logically bulletproof, we need an assumption that bridges 'high frequency of exposure' to 'influence on thought.' Look for a statement that says if someone is exposed to a massive amount of media, that media necessarily influences their habits of thought.