[Footnote ref 250]
According to the Sautrantika doctrine of Buddhism as described by Dharmakirtti and Dharmmottara which is probably the only account of systematic Buddhist logic that is now available to us in Sanskrit, inference (anumana) is divided into two classes, called svarthanumana (inferential knowledge attained by a person arguing in his own mind or judgments), and pararthanumana (inference through the help of articulated propositions for convincing others in a debate). The validity of inference depended, like the validity of perception, on copying the actually existing facts of the external world. Inference copied external realities as much as perception did; just as the validity of the immediate perception of blue depends upon its similarity to the external blue thing perceived, so the validity of the inference of a blue thing also, so far as it is knowledge, depends upon its resemblance to the external fact thus inferred (sarupyavas'addhi tannilapratitirupam sidhyati).
The reason by which an inference is made should be such that it may be present only in those cases where the thing to be inferred exists, and absent in every case where it does not exist. It is only when the reason is tested by both these joint conditions that an unfailing connection (pratibandha) between the reason and the thing to be inferred can be established. It is not enough that the reason should be present in all cases where the thing to be inferred exists and absent where it does not exist, but it is necessary that it should be present only in the above case. This law (niyama) is essential for establishing the unfailing condition necessary for inference [Footnote ref 251]. This unfailing natural connection (svabhavapratibandha) is found in two typesof cases. The first is that where the nature of the reason is contained in the thing to be inferred as a part of its nature, i.e. where the reason stands for a species of which the thing to be inferred is a genus; thus a stupid person living in a place full of tall pines may come to think that pines are called trees because they are tall and it may be useful to point out to him that even a small pine plant is a tree because it is pine; the quality of pineness forms a part of the essence of treeness, for the former being a species is contained in the latter as a genus; the nature of the species being identical with the nature of the genus, one could infer the latter from the former but not vice versa; this is called the unfailing natural connection of identity of nature (tadatmya). The second is that where the cause is inferred from the effect which stands as the reason of the former. Thus from the smoke the fire which has produced it may be inferred. The ground of these inferences is that reason is naturally indissolubly connected with the thing to be inferred, and unless this is the case, no inference is warrantable.
This natural indissoluble connection (svabhavapratibandha), be it of the nature of identity of essence of the species in the genus or inseparable connection of the effect with the cause, is the ground of all inference [Footnote ref 252]. The svabhavapratibandha determines the inseparability of connection (avinabhavaniyama) and the inference is made not through a series of premisses, but directly by the li@nga (reason) which has the inseparable connection [Footnote ref 253].
The second type of inference known as pararthanumana agrees with svarthanumana in all essential characteristics; the main difference between the two is this, that in the case of pararthanumana, the inferential process has to be put verbally in premisses.
Pandit Ratnakarasanti, probably of the ninth or the tenth century A.D., wrote a paper named Antarvyaptisamarthana in whichhe tried to show that the concomitance is not between those cases which possess the li@nga or reason with the cases which possess the sadhya (probandum) but between that which has the characteristics of the li@nga with that which has the characteristics of the sadhya (probandum); or in other words the concomitance is not between the places containing the smoke such as kitchen, etc., and the places containing fire but between that which has the characteristic of the li@nga, viz. the smoke, and that which has the characteristic of the sadhya, viz. the fire. This view of the nature of concomitance is known as inner concomitance (antarvyapti), whereas the former, viz. the concomitance between the thing possessing li@nga and that possessing sadhya, is known as outer concomitance (bahirvyapti) and generally accepted by the Nyaya school of thought. This antarvyapti doctrine of concomitance is indeed a later Buddhist doctrine.
It may not be out of place here to remark that evidences of some form of Buddhist logic probably go back at least as early as the Kathavatthu (200 B.C.). Thus Aung on the evidence of the Yamaka points out that Buddhist logic at the time of As'oka "was conversant with the distribution of terms" and the process of conversion. He further points out that the logical premisses such as the udahara@na (Yo yo aggima so so dhumava--whatever is fiery is smoky), the upanayana (ayam pabbato dhumava--this hill is smoky) and the niggama (tasmadayam aggima--therefore that is fiery) were also known. (Aung further sums up the method of the arguments which are found in the Kathavatthu as follows:
"Adherent. Is A B? (@thapana). Opponent. Yes.
Adherent. Is C D? (papana). Opponent. No.
Adherent. But if A be B then (you should have said) C is D. That B can be affirmed of A but D of C is false. Hence your first answer is refuted.")
The antecedent of the hypothetical major premiss is termed @thapana, because the opponent's position, A is B, is conditionally established for the purpose of refutation.
The consequent of the hypothetical major premiss is termed papana because it is got from the antecedent. And the conclusion is termed ropa@na because the regulation is placed on the opponent. Next:
"If D be derived of C.
Then B should have been derived of A.
But you affirmed B of A.
(therefore) That B can be affirmed of A but not of D or C is
wrong."
This is the pa@tiloma, inverse or indirect method, as contrasted with the former or direct method, anuloma. In both methods the consequent is derived. But if we reverse the hypothetical major in the latter method we get
"If A is B C is D.
But A is B.
Therefore C is D.
By this indirect method the opponent's second answer is reestablished [Footnote ref 254]."