Mental states comprise a diverse class, including perception, pain/pleasure experience, belief, desire, intention, emotion, and memory.
Intentionality-based approaches, on the other hand, see the power of minds to refer to objects and represent the world as the mark of the mental.
According to functionalist approaches, mental states are defined in terms of their role in the causal network independent of their intrinsic properties.
Some philosophers deny all the aforementioned approaches by holding that the term "mental" refers to a cluster of loosely related ideas without an underlying unifying feature shared by all.
Important distinctions group mental phenomena together according to whether they are sensory, propositional, intentional, conscious or occurrent.
An influential classification of mental states is due to Franz Brentano, who argues that there are only three basic kinds: presentations, judgments, and phenomena of love and hate.
Eliminativists may reject the existence of mental properties, or at least of those corresponding to folk psychological categories such as thought and memory.
Mental states play an important role in various fields, including philosophy of mind, epistemology and cognitive science.
This contrast is commonly based on the idea that certain features of mental phenomena are not present in the material universe as described by the natural sciences and may even be incompatible with it.
Another epistemic privilege often mentioned is that mental states are private in contrast to public external facts.
A repressed desire, for example, is a mental state to which the subject lacks the forms of privileged epistemic access mentioned.
[11] This position denies that the so-called "deep unconscious", i.e. mental contents inaccessible to consciousness, exists.
[12] Another problem for consciousness-based approaches, besides the issue of accounting for the unconscious mind, is to elucidate the nature of consciousness itself.
Opponents of consciousness-based approaches often point out that despite these attempts, it is still very unclear what the term "phenomenal consciousness" is supposed to mean.
[4][3][7] The originator of this approach is Franz Brentano, who defined intentionality as the characteristic of mental states to refer to or be about objects.
[21][22] Behaviorist definitions characterize mental states as dispositions to engage in certain publicly observable behavior as a reaction to particular external stimuli.
[24] A strong motivation for such a position comes from empiricist considerations stressing the importance of observation and the lack thereof in the case of private internal mental states.
This suggests that explanation needs to make reference to the internal states of the entity that mediate the link between stimulus and response.
Functionalists sometimes draw an analogy to the software-hardware distinction where the mind is likened to a certain type of software that can be installed on different forms of hardware.
Closely linked to this analogy is the thesis of computationalism, which defines the mind as an information processing system that is physically implemented by the neural activity of the brain.
[36][37] The closely related view of enactivism holds that mental processes involve an interaction between organism and environment.
A well-known classification is due to Franz Brentano, who distinguishes three basic categories of mental states: presentations, judgments, and phenomena of love and hate.
There is a great variety of types of mental states including perception, bodily awareness, thought, belief, desire, motivation, intention, deliberation, decision, pleasure, emotion, mood, imagination and memory.
Perception involves the use of senses, like sight, touch, hearing, smell and taste, to acquire information about material objects and events in the external world.
[40] It contrasts with bodily awareness in this sense, which is about the internal ongoings in our body and which does not present its contents as independent objects.
They are non-sensory cognitive propositional attitudes that have a mind-to-world direction of fit: they represent the world as being a certain way and aim at truth.
[44][45] They contrast with desires, which are conative propositional attitudes that have a world-to-mind direction of fit and aim to change the world by representing how it should be.
Emotions are evaluative responses to external or internal stimuli that are associated with a feeling of pleasure or displeasure and motivate various behavioral reactions.
Non-sensory states, like thought, rational intuition or the feeling of familiarity, lack sensory contents.
A mental state is conscious in this sense if the information it carries is available for reasoning and guiding behavior, even if it is not associated with any subjective feel characterizing the concurrent phenomenal experience.