The optimism vs. pessimism debate about the historical sciences is often framed in terms of arguments about the relative importance of overdetermination vs. underdetermination of historical claims by available evidence. While the interplay between natural processes that create multiple traces of past events (thereby conducive of overdetermination) and processes that erase past information (whence underdetermination) cannot be ignored, I locate the root of the debate in the epistemic granularity, or intuitively the level of detail, that pervades any historical claim justification network. To reveal the role played by granularity, I elaborate a model of historical claim justification. This model maps out the different elements that enter the justification of historical claims (incl., actual and inferred states of affairs, dating and information reconstructing theories). It also incorporates the different types of processes that affect traces of past events (information creating, preserving, modifying, and destroying processes). Granularity is shown to play a pivotal role in all elements of this model, and thereby in the inferred justification of any historical claim. As a result, while upward or downward shifts in granularity may explain changes about claims being considered as overdetermined or underdetermined, epistemic granularity constitutes an integral part of evidential reasoning in the historical sciences (and possibly elsewhere).

关于历史科学的乐观主义与悲观主义辩论通常是根据现有证据对历史主张的过度决定与不足决定的相对重要性的争论来构建的。虽然创造过去事件的多重痕迹（从而有利于过度决定）的自然过程与消除过去信息（从而导致不充分决定）的自然过程之间的相互作用不容忽视，但我将争论的根源定位在认知粒度上，或者直观地认为，细节，遍及任何历史索赔理由网络。为了揭示粒度所发挥的作用，我详细阐述了历史主张合理性的模型。该模型列出了历史主张合理性的不同要素（包括实际和推断的事态、年代测定和信息重建理论）。它还包含影响过去事件痕迹的不同类型的过程（信息创建、保存、修改和销毁过程）。粒度被证明在该模型的所有要素中发挥着关键作用，从而在任何历史主张的推断合理性中发挥着关键作用。因此，虽然粒度的向上或向下移动可以解释被认为是过度确定或不足确定的主张的变化，但认知粒度构成了历史科学（也可能在其他地方）证据推理的一个组成部分。