Yoga Sutra 1.18 samadhi follows on practice of the idea of stopping, and consists of samskaras alone

Sūtra I.18

The other (samādhi) follows on practice of the idea of stopping, and consists of saṃskāra-s alone

The words follows on practice of the idea of stopping show the relation to the discipline, but consists of saṃskāra-s alone explains its nature. They both go with The other, which therefore follows on the practice, and consists of saṃskāra-s alone. It is the seed-less ultra-cognitive samādhi, which is other than the cognitive samādhi which has just been defined in the previous sūtra.

stopping is ceasing. The compound idea-of-stopping (virāma-pratyaya) means: stopping and the idea of it; the form of the idea is simply stopping, so it is called the idea of stopping. It still has the form of an idea at the time of ceasing from everything, while it is still coming to a stop and before it has ceased to be an idea at all. In the same way a flaming fire which is little by little going down as its fuel is used up, is still truly flame until it finally becomes ashes.

The practice of this idea of stopping finally leads to a state, which must have been preceded by this practice, where only saṃskāra-s remain: with the stopping of the ideas, what remains is only the saṃskāra-s of them. The meaning is that when the mind has withdrawn from ideas of objects, there remain saṃskāra-s alone. The means to it is the higher detachment: the further degree of detachment is the means to this samādhi.

(Opponent) It should have been said, the higher detachment also, because it has just been said that the means to inhibition is by practice and detachment both.

(Answer) Not so. There could be no question that practice is one of the means, because the sūtra itself says practice of the idea of stopping. But there might have been a doubt about detachment, which was not mentioned, and in merely supplying that, it is not necessary to say ‘also’.

(Opponent) Well then, why is there no mention of detachment in the sūtra itself?

(Answer) It has been mentioned already.

(Opponent) Why was it mentioned there (and not here)?

(Answer) Because detachment was the context there, and it was mentioned in connection with the further (higher) detachment as distinct from the earlier one. The earlier detachment is confined to the field of the cognitive samādhi, and the remaining and higher detachment is a discipline with a different field, concerned only with the samādhi without seed (nir-bīja). So the sūtra did not use the word ‘detachment’, but the commentator indicates what is necessarily implied, because it has been declared, Their inhibition is by practice and detachment (I.12).

No meditation on an object can be a means to it, because that would be incompatible with this samādhi which has no object, whereas the idea of stopping, which is absence of anything is compatible with the samādhi with no object, and the meditation is on it. This is the samādhi without seed, with only saṃskāra-s remaining, which is ultra-cognitive.