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Thus, if it is known that a person has been exposed to sudden cold or has enjoyed a heavy feast, then, since it is known that cold leads to fever and over-feeding to indigestion, with the very first symptoms of uneasiness one may at once infer that the patient is likely to get fever or to have diarrhea or acute indiges- tion. Or, if it is known that the patient has a strong diarrhea, then it can similarly be inferred that he has eaten indigestible articles. Thus the two principal kinds of inference which were of practical use to the Ayur-veda physicians were inference of the occurrence of a disease from a knowledge of the presence of the causes of that disease, i.e. from cause to effect, and inference of the specific kinds of unhygienic irregularity from the specific kind of disease of the patient, i.e. from the effect to the cause. The other and third kind of inference is that of inference of disease from its early prognostications (pirva-riipa). Cakrapani, in commenting on the possibility of inference of specific diseases from their early specific prognostications, compares it with inference of rain from an assemblage of dark clouds or of the future rise of the Krttika constellation from the rise of the constellation Rohini, which immediately precedes it. Both these are cases of inference of future occurrences of causation or coexistence. The prognostica- tion may, however, be of the nature of an immediately and in- variably associated antecedent which may drop altogether when the disease shows itself. Thus before a high fever the hair of the patient may stand erect; this standing erect of the hair in a specific manner is neither the cause nor is it coexistent with fever, since it may vanish when the fever has actually come. It is, however, so invariably associated with a specific kind of fever that the fever can be inferred from it!. Again, when there is any doubt among a number of causes as to which may be the real cause of the disease, the physician has to employ the method of difference or 1 These two kinds of pirva-riipa are thus described by Cakrapani in his commentary on Caraka-samhita, 11. 1.7: tac ca pirva-riipam dvi-vidham ekam bhavi - vyadhy-avyakta-lingam...dvitiyam tu dosa -diisya-sammiirchand -janyam avyakta-lingad anyad eva yathda jvare bala-pradvesa-roma-harsadi. xin] Inductive methods in Ayur-veda 397 the method of concomitant variation for its proper ascertainment. That similar things produce the same kind of effects and opposite things produce opposite results are two of the accepted postulates of the law of sdémanya and visesa in the Caraka-samhita!. Now, applying these two principles, it is held that in a case of doubt as to any kind of irregularity being the cause of any particular disease it has to be found out by experiment whether the application of the suspected cause (e.g. cold) increases the disease (e.g. fever) ; if it does, and if the application of its opposite (e.g. heat) decreases the disease, then cold is to be regarded as the cause of the disease. If the application of any particular kind of element increases an effect (a particular kind of disease) and the application of its opposite decreases it, then tuat particular element may be regarded as the cause of that effect. Caraka holds that the three methods, viz. the cause and effect relation (nidana), the method of invariable prognostication (pirva-riipa) and the method of concomitant variation (upasaya, which includes anupasaya also) are to be employed either jointly or separately for the ascertainment of the nature of diseases which have already occurred or which are going to happen in the near future”. Caraka thus urges that the physician should examine carefully the causes of diseases by the application of all these methods, so that they may be ascer- tained from their visible effects. Caraka then goes on to give examples of a number of diseases and the causes or prognostica- tions by which their nature can be ascertained. He then says that a disease which is at first only an effect of some other causes - may act as a cause of other diseases and may thus be regarded both as an effect and asa cause. There is therefore no absolute difference between a cause and an effect, and that which is a cause may be an effect and that which is an effect may also in its turn be a cause. Sometimes a disease may behave as cause of another disease and then cease to exist itself, whereas again, one disease may exist side by side with another disease which it has produced and aggravate its effects. Then, again, a disease (cause) may produce a disease (effect), and that effect another effect. Thus one cause may produce one effect as well as many effects, and one effect may be due to one or to many causes, and 1 Caraka-samhitd, 1. 1. 44. ‘ 2 The other two methods of samprapti and riipa need not be discussed in this connection. 398 Speculations in the Medical Schools [cH. again many causes-may jointly produce many effects. Thus, though fever, delirium, etc. may all be produced by dryness (riiksa), yet under certain circumstances fever alone may be produced by it. Again, fever may also be produced by the combination of a number of causes which under other circumstances may produce jointly a number of diseases. So one entity may be an invariable con- comitant (liga) of one event or of many events, and there may also be a number of invariable concomitants of one event. Thus fever is the invariable concomitant of hygienic irregularities in general, and all-fevers have heat as their invariable concomitant. From certain kinds of hygienic irregularities fever can be inferred; but these can also be associated with a number of other diseases’. Hence it is evident that the determination of the nature of causes and effects and the inference of facts or events of invariable concomitance were an indispensable necessity for the Ayur-veda physicians in connection with the diagnosis of diseases and the ascertainment of their causes and cures. It was for this reason that Caraka divided inference into three classes, from causes to effects, from effects to causes and from the association of other kinds of invariable concomitants. The Nydaya-siitra of Aksapada contains expressions which seem to have been borrowed from Nagarjuna’s Madhyamika-kanika and from the Lankavatara-siitra and the regulations of Buddhistic idealism, and hence it is generally believed to have been composed in the second or the third century A.D.2 In this fundamental and earliest work of Nyaya philosophy inference (anumdna) is described as being of three kinds, viz. from cause to effect (piirvavat), from effect to cause (Sesavat), and in- ference from similarities (s@mdanyato-drsta) not comprehended under the cause-effect relation. Now it is exactly these three forms of inference that are described in the Caraka-samhita, and, so far as is known to the present writer, this is the earliest work which describes inference in such a systematic manner, and so it 1 See Caraka-samhita, 11. 8. 22-27. 2H. Ui’s The Vaisesika Philosophy, p. 16. L. Suali’s Filosofia Indiana, p. 14. Jacobi, article in ¥.4.O. Society, vol. xxxI, p. 29, 1911. A commentary on Nagarjuna’s Pramdna-vidhvamsana called Pramdna- vidhvamsana-sambhdasita-vrtit reproduces Nagarjuna’s definition of the cate- gories, which are the same as the categories enumerated in the first siira of Aksapada’s Nydaya-sitra. But, as Walleser points out in his Life of Nagarjuna from Tibetan and Chinese Sources, it is impossible to fix Nagarjuna’s date exactly. He may have lived at any time between the second and the fourth centuries a.D. So no fruitful result can be attained by considerations of this kind. XIIT] Logical Terms in Nydya and Ayur-veda 399 may naturally be regarded as the source from which Aksapada drew his ideas. Now Caraka’s work may be regarded as a revision of Agnivega’s work, based on Atri’s teachings, based on Bhara- dvaja’s instructions. Agnivega’s work is now lost, and it is not known what exactly were the contributions of Caraka in his re- vision of Agnivega’s work; but, since we find no work of an earlier date, Hindu, Buddhist or Jaina, which treats of the logical subjects found in the Caraka-samhita, and since these logical discussions seem to be inextricably connected with medical dis- cussions of diagnosis of diseases and the ascertainment of their causes, it seems very natural to suppose that Caraka got his materials from Agnivega, who probably got them from still earlier sources. Incidentally it may be mentioned that Jayanta, in his Nydya- mafyari, discussing the question of the probable sources from which Aksapada drew his materials, suggests that he probably elaborated his work from what he may have gathered from some other science (sastrantarabhyasat) ; but it is difficult to say whether by sastrantara Jayanta meant Ayur-veda. The Nydaya-siitra, how- ever, expressly justifies the validity of the Vedas on the analogy of the validity of Ayur-veda, which is a part of the Vedas}. The similarity of the Nydya-siitra definition of inference to Caraka’s definition is also very evident; for while the former begins tat-pirvakam tri-vidham (where tat-piirvakam means pratyaksa- piirvakam), the latter begins pratyaksa-pirvakam tri-vidham tri- kalam. But, while Caraka knows only the three forms of inference, he has no names for these three types such as are supplied by Aksapada, viz. piirvavat (related to pirva, the prior, or the cause), sesavat (related to Sesa, the later, or the effect) and samdanyato-drsta (from observed similarity in the past, present and future, which is also emphasized by Caraka in the same manner)?. From the con- 1 Mantrayurveda-pramanyavac ca tat-pramadnyam apta-pramanyat. Nydaya-sitra, 1. 1. 68.