  The second difficulty, however, applies to both versions of this approach, viz. accounting for the role played by rationes. The practice of precedent involves later courts being bound to either follow or distinguish the earlier decision, but only if the facts of the later case fall within the terms of the ratio. The ratio plays an indispensable role in fixing the scope of the later court's duty to follow or distinguish—it is only if the facts of the later case fall within the ratio that this question arises. This role is not appropriately captured by arguing that it is the justifications, and not the ratio, which are  binding.[12]   (Cf. Moore 1987, 185–7, 211–3). What the approach does help to highlight, on the other hand, is the role played in the practice of precedent by the justification for decisions. As noted above, determining the ratio is not a mechanical exercise: it involves understanding what was decided in a case—by reference to what was said in the judgment, earlier cases, and the general understanding of that area of the law. The precedent court's own justification for its decision plays an important role in determining the level of abstraction of the factors in the ratio, and for providing arguments for a narrower or wider reading of those  factors.[13]