'The behaviour, or rather the tendency towards certain patterns of behaviour should be built into the properties - or so it struck me. If that is the case, then we do not need laws as external rules telling properties how to interact; the laws would also be built into the properties. ... a propertied entity does not have to be doing things at all times; it has merely to be capable of doing them. So the intimate link between laws and properties suggests that properties should be considered as dispositions.'
(Alexander Bird (2007): Nature's Metaphysics. Laws and Properties, vii)
'Essentially dispositional properties are ones that have the same dispositional character in all possible worlds; that character is the property's' real rather than merely nominal essence. Categorical properties, on the other hand, do not have their dispositional characters modally fixed, but may change their dispositional characters ... across different worlds. ... Categoricalism about properties goes hand in hand with the view that the laws of nature are contingent and tell the properties what to do (or describe the patterns of regularity they happen to be parts of). Essentially dispositional properties have their identities fixed by their dispositional characters;'
(Alexander Bird (2007): Nature's Metaphysics. Laws and Properties, 44)
'Properties are categorical in the following sense: they have no essential or other non-trivial modal character. For example, and in particular, properties do not, essentially or necessarily, have or confer any dispositional character or power. Being made of rubber confers elasticity on an object, but it does not do so necessarily. Being negatively charged confers on objects the power to repel other negatively charged objects, but not necessarily. In other possible worlds rubber objects are not elastic, negatively charged objects attract rather than repel one another. The essential properties of a natural property are limited to its essentially being itself and not some distinct property.'
(Alexander Bird (2007): Nature's Metaphysics. Laws and Properties, 67)
'Thus everything attributable to the being of a categorical property is also attributable to the being of a potency. What distinguishes potencies is the additional claim that they have (essentially) a dispositional character. Thus there is more to the being of an essentially dispositional property than there is to that of a categorical property. In which case the claim that essentially dispositional properties are lacking in reality unless reducible to or explicable in terms of a 'decently real categorical property' is in error.'
(Alexander Bird (2007): Nature's Metaphysics. Laws and Properties, 103)
'Since S does not know whether water is H2O or not, S does not know whether S is in wH2O as opposed to wXYZ or some other such world. The thought is that it is this ignorance that leads to the illusion of metaphysical contingency in the case of identity propositions. As Kripke remarks (with my emphasis): '... it's true that given the evidence someone has antecedent to his empirical investigation, he can be placed in a sense in exactly the same situation, that is a qualitatively identical epistemic situation, and call two heavenly bodies "Hesperus" and "Phosphorus", without their being identical. So in that sense we can say that it might have turned out either way.' The sense of 'might' is not metaphysical; it is clearly a kind of epistemic 'might', but it is this that gives the illusion of metaphysical contingency. ... My hypothesis is that, ceteris paribus, epistemic contingency will give rise to the illusion of metaphysical contingency for other kinds of proposition too (e.g. law statements).'
(Alexander Bird (2007): Nature's Metaphysics. Laws and Properties, 179-180)