LewisianModal Realism is a well known theory whereby it is claimed that possibleobjects are concrete and are equivalently as real as we are or as the bed yousleep on.
It is noted that the most prevalent of these possible objects areworlds, which he says are maximally spatiotemporally related fusions ofconcrete objects (1986: 69:81). Lewis’ three doctrines explain his views uponthe existence of possible worlds, saying they exist and are alike our realworld. His second doctrine describes the possible worlds as having the samesort of things as our actual world, however, differing in content. This ultimatelybrings us to his third doctrine which states that worlds cannot be reduced tosomething more basic, as the are irreducible entities. It should be noted thatall possibilists accept the view that merely possible, non-actual entitiesexist. The LMR is ontologically and ideologically parsimonious and has been categorizedas being an economical theory. Lewis’ ontologycan be identified and separated into two categories, with the first being concreteobjects and the second; classes. Thestrongest argument in favour of modal realism is reductionism, which has beentaken to be a main strength of LMR.
Despite LMR being a very controversialtheory to accept, Lewis’ account of possible worlds provides us with a logicalanalysis of possibility and necessity, a view taken by Theodore Sider (2003:14).Looking through the analysis of possible worlds of modality, it can only beconsidered reductive, as Sider states, if the notion of truth in possibleworlds is non-modal; with it depending upon the ontological status of possible worlds(2003:8). As Lewis is able to distinguish the idea of possible worlds fromothers of the same kind it makes his argument reductive, whereas if he wasn’t ableto distinguish then it wouldn’t be. As aforementioned, Lewis is able todistinguish possible worlds from the actual world by defining possible worldsspatiotemporally. Lewis is able to reduce modality by separating the moderninterest towards possible worlds from it.
Reductionism is viewed as the mostfavoured argument in support of LMR since it overlooks modal claims, which areconsidered to cause conundrums.LMR isconsidered an extremely convincing and solid theory to follow, however, it isnot exempt from criticisms. A key objection comes from actualism, with the mainobjective coming from the actualist point of view that Lewis’ ontology is anincoherent argument. Sider recounts this objection in his book, ‘Reductive Theories of Modality’, notingthe objection is directed towards the existence of Lewis’ possible worlds(2003:17).
The objection is as follows that it is incomprehensible to suggestthe existence of absolutely anything being non actual. From an actualist pointof view, they are positing that the LMR’s possible worlds and accepting ofexisting things as non actual to be a very illogical as the term actual is aterm that loosely means everything. Sider takes the actualist view that if oneis to accept the possibility of Lewis’ world existing then it would be includedin actuality and wouldn’t relate to possibility and necessity (2003:17).
Theactualists criticism can be upheld as showing that the reductionist argumentmay not be the strongest for LMR.