Umberto Eco, The Search for the Perfect Language, Figure 10.3, p. Dogs are distinguished from wolves, and cats from tigers, on the basis of a dichotomy by taxonomic entities known as taxa (figure 10.3). ![]() This makes it difficult to know whether or not the same differences will be reproduced at some further point in the tree when it becomes necessary to specify the difference not just between dogs and cats, but also between violets and roses, diamonds and sapphires, and angels and demons.Įven taxonomy as practiced by modern zoology defines through dichotomies. In order to obtain new definitions, new differences need to be inserted into the diagram.īesides this, we can see that, although differences occur in one species, in this tree there are differences, such as “mortal/immortal,” which occur in two different species. Unfortunately this diagram does not tell us anything about the differences between dogs and cats, or horses and wolves, or cats and tigers. We see that the diagram defines a human being as a “rational and mortal animal,” which, in classical terms, is considered a satisfactory definition because there cannot be a rational and mortal animal which is not a human being, and only human beings are so. The terms in upper-case refer to genera and species while those in lower-case refer to differences, that is, to particular accidents which occur only in a given species. ![]() In figure 10.2, there is an example of how a Porphyrian Tree establishes the difference between human beings and gods (understood as natural forces) and between human beings and beasts. ![]() Umberto Eco, The Search for the Perfect Language, Figure 10.2, p. Each genus, with the addition of one of its divisive differences, produces an underlying species, which is so defined by its genus and its constitutive difference. In a Porphyrian Tree each genus is divided by two differences which constitute a pair of opposites. Such a structured representation was known in the Middle Ages as Porphyry’s Tree (because it was derived from the Isagoge of the Neo-Platonic philosopher Porphyry, living in the second-third century AD), and was still taken as a definitional model by the English searchers for a real character. To do this, it is necessary to insert differences into the classification.Īristotle, in his studies of definition, said that, in order to define the essence of a thing, we should select such attributes which “although each of them has a wider extension than the subject, all together they have not” ( Posterior Analytics II, 96a, 35). ![]() “Nevertheless, such a dictionary-like structure would not allow us to define the difference between a cat and a tiger, or even between a canine and a feline animal. This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author’s life plus 100 years or less. A Porphyrian Tree of logical relations, original c. Ramon Llull (1232-1315), Arbor naturalis et logicalis, Liber de logica nova, Valencia, 1512.
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