In his Yoga Sutras, Patanjali discusses the five kinds of vrittis, or fluctuations of consciousness. Vrittis are different types of thoughts or mental activities.
What are these five vrittis?

(The mental activities) are caused by valid knowledge (pramana), illusion (viparyaya), delusion (vikalpa), sleep (nidra), and memory (smriti).

Sutra 1.6, Light on the Yoga Sutras of Patanjali, B.K.S. Iyengar

Incorrect knowledge is when we think we know something, but are actually wrong. Conceptualization, delusion, or fantasy (vikalpa) is a condition in which our mind creates a perception that is not based on actual fact. A large portion of our thoughts is fantasies and images that are not based on reality. Our mind has the ability to create entire imaginary worlds, based in illusions (viparyaya).

In our daily life, we are constantly immersed in these vrittis. Patanjali writes that “Yoga is the cessation of the movements of consciousness” and that once the activity stops, the “one who sees” or the conscious principle of our being “dwells in its own true splendor” (Sutras 1.2 to 1.3). One can engage in long discussions and come up with various hypotheses about the concept of “cessation of the mental activity” as well as exactly what Patanjali meant by it. In any case, Patanjali does not rule out all mental activity and indicates (in sutra 1.5) “that the mental activity … can be painful or non-painful.”

In our daily life, we want our actions to be based on valid knowledge (pramana) and not invalid knowing (viparyaya) or empty images (vikalpa). While practicing asanas we can, through physical experience, awareness, observation, and correction establish correct knowledge.

For example, when we stretch in Urdhva Baddhanguliyasana, we want to extend the entire spine, in such a way that the back part will be equally extended as the front. But often, due to lack of sufficient shoulder joint flexibility or lack of awareness, we extend the front edge of the spine at the expense of the back, so that the back is actually shortened. This is an example of incorrect knowledge. We think we are extending, while in fact, we are shortening. In reality, we extend our front spine and shorten the back spine. One of the reasons for this is that our body awareness is lacking – we are aware to a greater extent of the front of our body, simply because we see it – what happens in the back, is largely non-existent for us and is therefore invalid knowing (viparyaya).

In order to bring awareness to the back, we can practice the pose with our back to a wall (or a corner of a wall). Then, we can use our sense of touch to understand the positioning of our back. By bringing awareness to our back, we can correct our incorrect knowledge, and learn how to equally stretch our front and back spine, and move from viparyaya to pramana.

Such practice that cultivates awareness can develop valid knowledge about an important part of reality – our body. By correctly perceiving our body’s positioning in space and the various activities we do with it, we are opening the correct perception of what is right and wrong in other parts of our experience. Therefore, a correct practice that is done with reflective observation can repair and provide us, through physical experience, a sense of distinction between right and wrong. It can help dispel invalid knowledge (viparyaya). Such a capability is the basis for establishing pramana – a valid perception of reality.

What makes up Pramana?

Patanjali says about pramana: “valid knowledge is direct (pratyaksha), inferred (anumana) or proven as factual (agama).” When we start to practice, we have no direct perception based on sensory data and we also often have invalid knowledge (viparyaya). At this point we need to rely on external evidence, that is, to listen to what the teacher tells us, or read books on yoga and learn from them (agama). Later, when we begin to recognize the issue, we can draw conclusions or rationally infer about it (anumana). Only when we become skilled and mature can we reach a direct intuitive perception of the reality we experience (pratyaksha).

Iyengar tells of his path of yoga and says:

By reversing the sutras 1.7 of Patanjali, I learned the importance of the sadhana. I took each asana, whether it is Utthita Trikonasana, Tadasana, or Vrschikasana as a spiritual scripture (agama). For me, each asana became a literary book. Knowing that each asana is an archetypical icon of the body, I worked to get that fineness in each one.  For this I used the middle guideline of Patanjali, to apply my own logical imagination (anumana). Then, I practiced using the pros and cons in different ways. Suddenly, I experience naturalness, concord, grip, and rhythm with various parts of the body, and lightness in mind. This feel of concord in body and lightness in mind led me to valid knowledge (pramana). This valid knowledge led me to intuitive perception (pratyaksha-pramana).

Astadala Yoga Mala, Vol. III, p. 67