1.4 vṛtti-sārūpyam itaratra
While in the state of samadhi, consciousness is experienced in its pure state, at other times there is an apparent union, conjunction or merging of consciousness with the mind.
Contrary to the most popular definitions of yoga - ie yoga is union, union of the individual soul with the universal soul, union of the mind with god etc., Patanjali says that union (of consciousness with mind) is the problem and dis-union of consciousness from the mind is the solution.
The fourth chapter of the Yoga Sutra is called the Kaivalya Pada - the chapter on isolation or aloneness. The soul, or purusha is experienced in isolation or separate from mind and body in the state of samadhi.
Union of consciousness with mind is also called ego or asmita in the yoga sutra - this union is the primary obstacle to be overcome.