Step 1: Understanding the Concept:
The question asks for an inference about effective advertising strategy, based on the principles of belief discussed in the passage.
Step 2: Detailed Explanation:
The passage begins by establishing a fundamental condition for belief: "the question of belief is valid only for those propositions that are understandable." It then defines an understandable proposition as one "that is expressed using correct grammar and known words."
Regardless of whether the Cartesian or Spinozan model is correct, the first and most essential step for a proposition to even be considered for belief is that it must be understood by the recipient. If an advertiser uses unfamiliar words, the customer will not understand the proposition, and the question of believing the advertisement becomes moot.
Let's consider the other options:
(B) traditional motifs: The passage does not discuss cultural motifs.
(C) negative words: The passage does not discuss the impact of positive or negative framing.
(D) & (E) not distract or overwhelm the customer: According to the Spinozan hypothesis (which the author leans towards), distraction and cognitive load make disbelief *harder*. This means a distracted or overwhelmed customer is *more* likely to believe an ad, not less. Therefore, an advertiser might actually want to use distracting images or overwhelming information to prevent the effortful process of doubt. These options suggest the opposite of what could be inferred.
Thus, the most fundamental and undeniable step an advertiser must take, according to the passage, is to ensure their message is understandable.
Step 3: Final Answer:
Using familiar words ensures the proposition is understandable, which is the necessary first condition for belief to occur.