cannot be in identical physical states, due to their different composition and structure, can nevertheless be in identical psychological states. Some philosophers refer to this argument — that multiple realizability is much more likely than reductionism — as the likelihood argument. The a priori argument Putnam also formulates a complementary argument based on functional isomorphism. He defines the concept in these terms: "Two systems are functionally isomorphic if there is a correspondence between the states of one and the states of the other that preserves functional relations." Two computers, for example, are functionally isomorphic if the sequential relations among states in one are exactly mirrored by those in the other. A computer made of electrical components and a computer made of cogs and wheels can be functionally isomorphic even though they are constitutionally different. Functional isomorphism implies multiple realizability. Some philosophers refer to this as the a priori argument. Arguments against multiple realizability Some philosophers deny that mental states are multiply realizable. A detailed examination of how brain areas are identified in neuroscience shows that psychological functions are not, in fact, multiply realizable. Arguments against the significance of multiple realizability Some philosophers accept the thesis that mental states are multiply realizable but deny that multiple realizability gives rise to functionalism or other forms of non-reductive physicalism. Reductionism in other sciences Early objections to multiple realizability were limited to the narrow, "across structures-type" version. Starting with David Kellogg Lewis, many reductionists argued that it is very common in scientific practice to reduce one theory to another via local, structure-specific reductions. A frequently cited example of this sort of intertheoretic reduction is temperature. The temperature of a gas is identical to mean molecular kinetic energy. Temperature in a solid is identical to mean maximal molecular kinetic energy because the molecules of a solid are more restricted in their movements. Temperature in a plasma is a mystery because the molecules of a plasma are torn apart. Therefore, temperature is multiply realized in a diversity of microphysical states. Disjunction Jaegwon Kim argues that disjunction — the idea that the physical realization of a particular mental state is not a particular physical state but the disjunction of the physical states that realize that mental state — creates problems for multiple realizability. Putnam also argued against this "disjunctive" possibility in later work. Block and Fodor had also argued against it. Causal closure of the physical Kim