When is a belief justified, or an operation justifying? Hume’s practice rests on the assumption that an operation is justifying when it is reliable. A systematic review of Book I shows that Hume is persistently concerned to judge the reliability of our operations. Here are a few examples: methods in geometry are fallible (T 71);7 the observations and inferences concerning the three philosophical relations which can vary without a change in ideas are fallible (T 73); “When the imagination from any extraordinary ferment of the blood and spirit, acquires such a vivacity as disorders all its powers and faculties, there is no means of distinguishing betwixt truth and falshood” (T 123); “our confidence in the veracity of that faculty [memory] is the greatest imaginable and equals in many respects the assurance of a demonstration” (T 158); “Our reason must be consider’d a kind of cause, of which truth is the natural effect” (T 180); introspection leading to the belief that a given state is a perception is infallible (T 190); and “whatever ideas place the mind in the same disposition or in similar ones, are apt to be confounded” (T 203). These and many similar passages make it difficult to avoid the conclusion that Hume’s central concern in epistemology is the assessment of the reliability of operations. Since his central concern is also the assessment of justification, it is plausible to see him as defining justifying operations as reliable ones.8 The attribution of reliabilism is confirmed by the correlation in the text between talk of justified belief (perceptions) or justifying operations and talk of true belief (perceptions): “We may draw inferences from the coherence of our perceptions, whether they be true or false; whether they represent nature justly, or be mere illusions of the senses” (T 84); “What, then, can we look for from this confusion of groundless and extraordinary opinions but error and falshood? And how can we justify to ourselves any belief we repose in them?” (T 218).9