Pragmatism = Pragmatism is an idea or thought such that usefulness and things that can be practiced or manipulated or handled are the most important things.
Substance Dualism = Substance Dualism is a mind-body dualism such that mind and body are distinct substances.
Physicalism = Physicalism is an idea that everything, including mind and body, is ultimately physical, and can be explained by contemporary physics.
Mental = Mental is the set of things, phenomena, etc, directly related to thoughts, perceptions, etc.
Physical = Physical is the set of things, phenomena, etc, directly related to movements of objects, neural states, brain processes and states, etc.
Now, let's jump into the problems of substance dualism. Substance dualism claims that there are two kinds of substances: mind and body. However, the very term 'substance' is a classic term originated from modern era of 16th-17th centuries, probably. So, instead of using the term 'substance dualism', there is no problem of using the term 'type dualism' safely. Now, the term 'substance dualism' is substituted into 'type dualism', and redefined as follows:
Type Dualism = Type Dualism is a mind-body dualism such that there are distinct-fundamental types into two kinds: mind-type and body-type.
The version of type dualism of mind-body things is, in fact, the same as Cartesian dualism. The so-called Cartesian dualism is a theory including following definitions:
Cartesian mind = Cartesian mind is a thing that is made up of immaterial, non-physical, non-spatio-temporal thoughts.
Cartesian body = Cartesian body is a thing that is located in a spatio-temporal point or such points by being extended in spatio-temporal points.
Now, the combination of type dualism and Cartesian dualism is Cartesian type mind-body dualism, defined as:
Cartesian type mind-body dualism = Cartesian type mind-body dualism is a set of ideas such as (i) endorsing two distinct types constituting the world as mind and body, and (ii) embracing immaterial, non-physical, non-spatio-temporal nature of mind, and material, physical, spatio-temporal nature of body.
Now, all key terms are ready. It's the time that we are going to examine the very problems of Cartesian type mind-body dualism by a possible scenario as follows:
In other words, the fact that we can think like "there is a red tomato over there" when we see or look at the red tomato is a definite proof of which Cartesian type mind-body dualism is false. So, the more formal argument goes as follows:Robert is a Cartesian type mind-body dualist. One day, he is in the situation of looking at some red tomato. The red tomato that Robert is looking at is, of course, a physical object located in such and such and such space-time points. Now, the neural states and the brain states of Robert are working such and such and such for making such and such and such visual perceptions perceived by Robert. All the neural-brain states of Robert are located in such and such and such space-time points, like the tomato that Robert is looking at. Unfortunately, however, the Cartesian mind of Robert is not located in any space-time point. Robert's body, including his neural states and brain states, is only working in space-time points, but his mind is not working in any physical world. This means that his body, including neural states and brain states can contact with the red tomato, but his mind cannot be related to the physical-space-time-point-located-red tomato!!! Our poor Robert cannot have, therefore, a thought like "there is a red tomato over there," "Robert thinks that there is a red tomato over there," etc. Even his mind is not perceiving that there is a red tomato, since mind is not in space-time points, but only his body-neural-brain things with the red tomato are in space-time points.
(1) If Cartesian type mind-body dualism (i.e. Substance dualism) is right, then there cannot be mental states.
(2) There can be mental states.
Therefore, (3) Cartesian type mind-body dualism is wrong.
This argument against mind-body dualism is formally taking modus-tollens formulation, and so formally valid. The argument is called 'a pragmatist argument against substance dualism' in that we can easily accept that refuting dualism and embracing monism are better and more useful (appealing to usefulness), and that we can manipulate, or handle, or practice, etc. our perceptions and thoughts when we abandon dualism.