Together they refer to one's mental processes as a whole. Separately, what are they and how are they different?
'Citta' (the C is pronounced as ch in cheetah) is a generic word for mind, including thoughts as well as emotional state. When the Chinese translated Buddhist texts they often used 'shin', the heart-mind, to indicate citta.
'Manas' (both As are pronounced as in Adam) is the "inner eye" that can see thoughts, memories, and one's state of mind (citta).
'Vijnana' (jna is pronounced as jnya - i.e. with soft n) is experience of reality that arises from mind's ability to recognize and interpret new stimuli by relating and comparing them with memories of past experiences.
This is what i've gathered from reading about this in the Plum Village (Thich Nhat Hanh) tradition and from my own experience. Please feel free to update and improve, i am not sure about everything
The eight conciousnesses
There are eight consciousnesses (not counting Vijnana which is split into six parts):
- Eye Consciousnesses
- Ear C.
- Nose C.
- Tongue C.
- Body C.
- Mind C.
- Citta (Store C.)
The "top level" of conciousness - we are most conscious of the experiences happening in this part of the mind
The first five c.
The first five consciousnesses have access to "reality in itself" with no discrimination/dualism (me and you, subject and object, etc). They are in "direct contact" with reality. They are not distorted by our thinking and our past experiences.
The sixth c.
The sixth conciousness "mind" is the part of our mind with ideas and it has access to (at least parts of) all the seven other conciousnesses. When the sixth conciousness collaborates with the first five the connection with "reality in itself" is interrupted
The sixth is itself suspended for example while sleeping without dreaming. When dreaming the sixth is active and gets all it's information from the eigth conciousness (Citta)
Strongly connected with the sixth conciousness (mind c.), it grasps at experiences
In the seventh consciousness there are four basic afflictions: self-delusion, self-love, self-view, and self-conceit. The basic illusion inherent in all four afflictions is the illusion about self: this body is mine, is me; this feeling is me; these emotions are me; this consciousness is me and I am independent from everything else
Unconcious, contains all experiences we've had, all is stored here
I drew the picture below for our Sangha group where we brought up manas and am happy to share it here. The image contains an example where a seed in the store (Citta) has been watered (maybe by something we have seen or heard together with our perceptions) and that seed has manifested in the mind consciousness
Manas is past mind, citta is future mind, and vijnana is present mind. Sometimes it's also said that manas is fore-running, citta far-going, and vijnana is birth-relinking activity of mind.
Also, manas is supporting (subsequent) and thinking/contemplating aspect of mind, citta is accumulating and diversity aspect of mind (it's increase with defilements or cease without them), and vijnana is cognizing aspect.
In Yogacara citta is equated with alaya-vijnana (storehouse consciousness), manas with klista-manas (defiled mind), and vijnana with pravritti-vijnana (functioning mind).
ever seen a buddhist prayer wheel? that's the citta,the little ball at the end of the string. the object itself is the metaphor.
when you still the mind using concentration, and at the same time observe the mind using mindfulness, then you will observe the spinning citta. as you focus on the citta more, you will bring it to rest.
it has no mass, and so it has no inertia. it can spin up to mhz in a fraction of a second, the moment thought arises and is let through by the observer. in this way the spin of the citta can be controlled.
While there have been many attempts to show that these are either the same or different, in my view that is missing the point somewhat. The terms are, generally speaking, synonyms, and their usage overlaps to some degree, but they tend to be used in different contexts:
Viṇṇāṇa is part of the khandhas and āyatanas, and hence pertains to the first noble truth: it is suffering.
Mano is typically used in an active sense of will or volition, closely related to kamma, and hence pertains to the second noble truth, the cause of suffering .
Citta is to be developed and thus pertains to the fourth noble truth. The cessation of all these is, of course, the third noble truth.
There is a great lack of agreement among scholars in translating. This study tries to seek some clarity between the three terms:
Citta: The mirror of mind that lacks any qualities of it's own, but provides the canvas for the phenomena of samsara and nirvana (synonymous with the all-ground consciousness in Yogachara, though here being referred to in it's mundane aspect, as it appears to ordinary beings). It is also considered to be the domain where karmic tendencies rest dormant, but with the possibility of manifesting when exposed to an external stimuli that generates grasping and conceptualization (which is the function of manas).
Caitta: The qualities of the mind. The waves on the ocean, the coloring of a gem with a colored cloth beneath it, etc. The basic dispositional sense that the mind is imbued with. For more info see the 51 mental factors.
Vijnana: the basic sense of self-orientation and "I-making" that infuses the experience of reality for unenlightened beings. It is differentiated into six forms given the six classes of phenomena (sight, sound, touch, taste, smell, and ideation). It is the projection of an illusory "I" in reference to these phenomena. The basis of this reference is the citta, which itself has no self-qualities (though it can become anything). This is what the Buddha propounds anatman.
Manas: Conceptual thinking. Can be afflictive or non-afflictive. Vijnana (a basic self-orientation toward reality), is a necessary precondition for the functioning of conventional manas. This is the part of the mind that believes in the solid, unchanging, self-nature of phenomena and conceptualizes about their various inter-relations. Whether there is still conceptualization within enlightenment (with the transcendence of vijnana) is argued about, but the most sensible description is that conceptualization occurs, but those concepts are not experienced as solid and unchanging, but are seen as the play of interdependent phenomena, none of which possess their own self-nature.