Final answer:
Doubt is negative when it leads to extreme skepticism that prevents gaining knowledge or when it is based on insufficient evidence, resulting in premature conclusions. It also becomes counterproductive when it ignores the 'no defeaters' condition in justifying true beliefs.
Step-by-step explanation:
Doubt is considered negative when it prevents us from acquiring knowledge or acting upon justified beliefs. A classic example is the philosophical skepticism that questions whether we can truly know anything, as exemplified by the 'brain in a vat' argument. Such extreme skepticism, requiring certainty for knowledge, is often viewed negatively because it can inhibit the pursuit of truth and understanding.
Another example where doubt can be negative occurs when it is based on insufficient evidence, leading to hasty conclusions about the general case, like assuming a restaurant is bad after only two visits. A related concept is the burden of proof in logic, which highlights that the one making an affirmative claim, not the one doubting, must provide evidence to support their assertions.
Moreover, doubting without considering the 'no defeaters' condition in epistemology can lead to rejecting knowledge unjustifiably. For instance, if we have strong enough evidence to support our belief but are unaware of minor contradictory evidence, this should not necessarily undermine our justified true belief. Rigorous application of doubt can obstruct the acquisition and consolidation of knowledge.