These positions make use of the philosophical type–token distinction (e.g., Two persons having the same "type" of car need not mean that they share a "token", a single vehicle).
Proponents of these views argue that in the same way that talk of demonic possession was questioned with scientific advance, categorisations like "pain" may need to be revised.
Logical behaviorism emerged as a serious contender to take the place of the Cartesian "ghost in the machine" and, although not lasting very long as a dominant position on the mind/body problem, its elimination of the whole realm of internal mental events was strongly influential in the formation and acceptance of the thesis of type identity.
There were actually subtle but interesting differences between the three most widely credited formulations of the type-identity thesis, those of Place, Feigl and Smart which were published in several articles in the late 1950s.
Putnam's invocation of multiple realizability does not, of course, directly answer the problem raised by Smart with respect to useful generalizations over types and the flexible nature of the type-token distinction in relation to causal taxonomies in science.
Another frequent objection is that type identity theories fail to account for phenomenal mental states (or qualia), such as having a pain, feeling sad, experiencing nausea.
A famous formulation of the qualia objection comes from Frank Jackson[8] in the form of the Mary's room thought experiment.
Let us suppose, Jackson suggests, that a particularly brilliant super-scientist named Mary has been locked away in a completely black-and-white room her entire life.
Over the years in her colour-deprived world she has studied (via black-and-white books and television) the sciences of neurophysiology, vision and electromagnetics to their fullest extent; eventually Mary learns all the physical facts there are to know about experiencing colour.
The type identity theorist, such as Smart, attempts to explain away such phenomena by insisting that the experiential properties of mental events are topic-neutral.
If one were to hear these terms alone in the course of a conversation, it would be impossible to tell whether the topic under discussion concerned geology, physics, history, gardening, or selling pizza.
For the identity theorist, sense-data and qualia are not real things in the brain (or the physical world in general) but are more like "the average electrician."