 That said, on the other hand, there certainly is no development of a modal logic of necessity and possibility and talk of possible worlds in Dharmakīrti, nor in Indian philosophy generally for that  matter.[25]  Although Buddhist Epistemologists do often talk of non-existent things, like rabbit’s horns (śaśaviṣāṇa), it is far from clear that they would predicate positive properties (say, sharpness) of them in such and such possible situations or “worlds.” What then is the force of the “must” in the smoke-fire cases, and more generally when terms have a “nexus” so that one will not be without the other? Words that are typically used in these kind of Dharmakīrtian discussions are niścaya (certainty) and avyabhicāra (not-deviating). Many modern interpreters have used the term “necessity” in interpreting these and related terms (See e.g., Dunne 2004, ch. 3; Iwata 2004); this might lead one to think that when F and G have a nexus, it is a necessary truth (i.e., true in all possible worlds) that for all x, if x is F then x is G. A more likely interpretation, however, is that Dharmakīrti is dealing with the actual world and that these key terms are to be interpreted epistemically in terms of justification: given such and such natural connections between F and G, we can be sure that for all x, if x is F then x is G. Taking niścaya in this way, his point would not be about metaphysical necessity throughout worlds but more about justified very strong confidence that a universally quantified material implication holds without exception in the actual world because of natures in this  world.[26]