disposition a tendency of an object or system to act or react in characteristic ways in certain situations. Fragility, solubility, and radioactivity are typical physical dispositions; generosity and irritability are typical dispositions of persons. For behaviorism, functionalism, and some forms of materialism, mental events, such as the occurrence of an idea, and states such as beliefs, are also dispositions. Hypothetical or conditional statements are implied by dispositional claims and capture their basic meaning: the glass would shatter if suitably struck; left undisturbed, a radium atom will probably decay in a certain time; etc. These are usually taken as subjunctive rather than material conditionals (to avoid problems like having to count as soluble anything not immersed in water). The characteristic mode of action or reaction – shattering, decaying, etc. – is termed the disposition’s manifestation or display. But it need not be observable. Fragility is a regular or universal disposition; a suitably struck glass invariably shatters. Radioactivity is variable or probabilistic; radium may or may not decay in a certain situation. Dispositions may also be multitrack or multiply manifested, rather than single-track or singly manifested: like hardness or elasticity, they may have different manifestations in different situations. In The Concept of Mind (1949) Ryle argued that there is nothing more to dispositional claims than their associated conditionals: dispositional properties are not occurrent; to possess a dispositional property is not to undergo any episode or occurrence, or to be in a particular state. (Coupled with a positivist rejection of unobservables, and a conception of mental episodes and states as dispositions, this supports the view of behaviorism that such episodes and states are nothing but dispositions to observable behavior.) By contrast, realism holds that dispositional talk is also about actual or occurrent properties or states, possibly unknown or unobservable. In particular, it is about the bases of dispositions in intrinsic properties or states: fragility is based in molecular structure, radioactivity in nuclear structure. A disposition’s basis is viewed as at least partly the cause of its manifestation. Some philosophers hold that the bases are categorical, not dispositional (D. M. Armstrong, A Materialist Theory of Mind, 1968). Others, notably Popper, hold that all properties are dispositional.
See also BEHAVIORISM , COUNTERFACTU- ALS , PHILOSOPHY OF MIND , PHILOSOPHY OF SCIENCE , PROPENSITY, STAT. D.S.