To a novice like me, chitta in chittanupassana and dhamma in dhammanupassana seem like similar category of phenomena being contemplated. Can someone please explain how they are distinct?
In the four foundations of mindfulness the third is contemplation of the state of mind (different from a single thought):
"And how is a monk skilled in reading his own mind? Imagine a young woman — or man — fond of adornment, examining the image of her own face in a bright, clean mirror or bowl of clear water: If she saw any dirt or blemish there, she would try to remove it. If she saw no dirt or blemish there, she would be pleased, her resolves fulfilled: ‘How fortunate I am! How clean I am!’ In the same way, a monk’s self-examination is very productive in terms of skillful qualities: ‘Do I usually remain covetous or not? With thoughts of ill will or not? Overcome by sloth & drowsiness or not? Restless or not? Uncertain or gone beyond uncertainty? Angry or not? With soiled thoughts or unsoiled thoughts? With my body aroused or unaroused? Lazy or with persistence aroused? Unconcentrated or concentrated?’
“If, on examination, a monk knows, ‘I usually remain covetous, with thoughts of ill will, overcome by sloth & drowsiness, restless, uncertain, angry, with soiled thoughts, with my body aroused, lazy, or unconcentrated,’ then he should put forth extra desire, effort, diligence, endeavor, relentlessness, mindfulness, & alertness for the abandoning of those very same evil, unskillful qualities. Just as when a person whose turban or head was on fire would put forth extra desire, effort, diligence, endeavor, relentlessness, mindfulness, & alertness to put out the fire on his turban or head; in the same way, the monk should put forth extra desire, effort, diligence, endeavor, relentlessness, mindfulness, & alertness for the abandoning of those very same evil, unskillful qualities.”
—Anguttara Nikaya 10.51
The fourth foundation is contemplation of five categories of dhamma under the overarching four noble truths. There is particular opposition there between the five hindrances and the seven factors of awakening, the former to be overcome, the latter developed. These are active processes for application, and one of the important ones is described under the five hindrances:
“He discerns how there is the arising of unarisen sensual desire. And he discerns how there is the abandoning of sensual desire once it has arisen.15 And he discerns how there is no further appearance in the future of sensual desire that has been abandoned.”
—Majjhima Nikaya 10, Digha Nikaya 22
The fourth foundation is applied to the third as in Anguttara Nikaya 10.51, where having diagnosed the condition the practitioner puts forth extra effort as instructed in Samyutta Nikaya 46.51, and the well known Majjhima Nikaya 20.
Imagine a basin of water, and take the water as an analogy for citta.
When you’re watching the water with your face dip into the water, that’s cittānupassanā. When you’re watching the water with your face lifted off the water, that’s dhammānupassanā.