[b]II, 19 vivesa avisea lingamatra alingani guna parvani

The stages of manifestation
of the primal forces of desire are fourfold:
specific differentiation of subject and object,
nonspecific differentiation of subject and object,
with form, an awareness of an object?s direct essence,
and without form, a state of superconsciousness.[/b]

M. Stiles

Nature (Prakriti) can be
a) alinga (without mark or form): in this state, nature is unmanifest and the gunas are balanced (sattvic). This form of Prakriti can only be perceived by the Seer and it has no effect on matter.
b) linga ( with mark or form): in this state, the gunas are imbalanced which results in the manifestation of prakriti but it is still in a subtle form that is imperceptible by the senses and the intellect.
c) avisea (abstract): the manifestation of nature that is perceived by the intellect.
d) visea (concrete): the manifestation of nature that is perceived by the senses.

Swami Satchidananda explains that ?Normally we only understand things that we can see. However, if we develop a subtler perception we can also see subtler things. For instance, we can see a flower but we can only sense the smell… Even the smell is matter, although very subtle; and if we have developed subtle enough perception, we can see it emanating like a magnetic force. Although each individual has an aura, we normally see bodies but not their auras, the colors of their aural bodies. But we can develop the subtle senses to see them.

Iyengar, B.K.S., Light on the Yoga Sutras of Patanjali. New Delhi, India: Harper Collins Publications India. 1993

Swami Satchidananda, The Yoga Sutras of Patanjali. Buckingham, VA: Integral Yoga Publications. 2004
Swami Shyam, Patanjali Yog Darshan, India: International Meditation Institute, 2001, 3rd. edition.

Stiles, M., Yoga Sutras of Patanjali. Boston, MA: Red Wheel/Weiser LLC. 2002