Ibn Sina, in contrast to
al-Kindi who did not define hadd
(definition), begins his book of definitions with the definition of hadd. In the introductory matter of the treatise before the technical definitions, Ibn Sina discusses definition in a discursive manner, somewhat reminiscent of
al-Farabi’s discussion of definition in The Book of Letters.
Ibn Sina says that in true definitions logic guides in demonstrating the quiddity of a thing, the perfection of its essential existence, with no separation of the essential predicates of a thing from it, unless they are included either in actuality or in potentiality. Such a definition is in reality equal to the thing defined.
In comparing Ibn Sina on definition with al-Farabi on definition, there are some remarkable similarities. While al-Farabi writes about al-hudud al-yaqiniyya (certain definitions), Ibn Sina discusses al-hudud al-haqiqiyya (real definitions).13 For Ibn Sina definition is:“a signification (dalla) of the essence of the thing.”14 For al-Farabi definition is used:“in signifying (dalala) how to distinguish the thing.”15 Thus, for both philosophers, the purpose of definitions is to signify, or indicate something. For Ibn Sina it signifies the essence of something; for al-Farabi it signifies the distinction of something from something else. They both use the same root, dalla, meaning “to signify, indicate,” although in different forms. At this point, Ibn Sina says that a definition is complete (kamal) under certain circumstances. Al-Farabi has begun this section referring to a complete (kamal) definition.
Furthermore, as mentioned in Chapter 3, al-Farabi says that while studying the four causes one will learn the essence of a thing and thus its definition. While not specifically relating definition to four causes, Ibn Sina still emphasizes that form and matter combine to generate the essence of a thing which is defined – so at least two of the causes (formal and material) are worked into his theory ofdefinition. Al-Farabi says of definition, “. . . it is considered that there is no difference between a thing and its definition.”16 Ibn Sina says, “When a definition is thus it is equal to the defined thing in reality.”17 Consequently it is clear that Ibn Sina has relied on al-Farabi for his ideas about essential definitions. Ibn Sina explicitly indicates his debt to Aristotle in the Topics in his technical definition of hadd. The definition of definition is what the wise man (Aristotle) mentions in the book, Topics: it is a statement indicating (pointing to) the quiddity (mahiyya) of a thing, that is, regarding the perfection of its essential existence. It (definition) is what is obtained from its proximate genus and its differentia ( fasl).
The italicized portion of the definition is quoted from Aristotle’s definition in Topics. The second part is paraphrased from Porphyry’s Eisagoge. The definition of rasm, usually translated as “description,” follows the definition of definition (hadd). In al-Ilahiyyat, Ibn Sina discusses definitions and what exactly they signify in detail. After stating that both matter and form are found in definition he says: . . . ather it is a combination of form and matter (madda), for this is what the composite is; and quiddity is this composition.
So form is the one to which composition is added, and quiddity is this self-same composition that combines form and matter. The unity arising from the two of them is through this one.
In this definition Ibn Sina states one of the basicphi losophical problems, the relationship of form and matter. Here he states that both form and matter unite to compose the quiddity or essence of a thing, and this essence must be defined in a definition. If definitions define both form and matter, then true definitions yield knowledge of real things.
Ibn Furak (d. 1015), who wrote definitions of Islamictheolo gy and law, gave this definition of definition: “It is a statement distinguishing between the thing defined and what has nothing to do with it in any way.” This demonstrates the strong contrast between Ibn Sina’s philosophical definition, which particularly indicates the use of definitions to search for the essence of things and the point of view of a jurisprudent who initially takes an ordinary language approach. This comparison is interesting because Ibn Furak is a close contemporary of Ibn Sina, but Ibn Furak’s definition reflects his professional bias, rather than his era.