The reason for calling drowsiness, worry, selectiveness and discursiveness 'the four variables' is that they become positive, negative, or indeterminate according to the level and quality of the mental situation. Generally, the emotionally tainted drowsiness, worry, selectiveness and discursiveness obstruct every aspect of the positive -- specifically, the three kinds of higher training.
The five obscurations, stated in the Sutras, are expressed by Arya Nagarjuna (Suhrllekha, 44) as follows:
Ebullience, worry, a mind to injure (malice), sluggishness,The five obscurations are counted as five because ebullience and worry are considered as one obscuration; drowsiness and sluggishness are also considered as one; and a mind to injure, attachment, and doubt are counted individually.
Drowsiness, cupidity-attachment, and doubt --
Know well that these five are the thieves
Who rob one's wealth of the positive.
These five obscurations, such as drowsiness, mean that, in general, all positive (training) and, in particular, the three kinds of higher training, are obscured. Attachment and a mind to hurt obscure the higher training in self-discipline. Drowsiness and sluggishness, ebullience and worry obscure mental training. Doubt, selectiveness and discursiveness obscure training in appreciative discrimination.
The Abhidharmasamuccaya says that by these five obscurations, rules of self-discipline and concentration are obscured, but the Samvaravimsakatika says that only concentration is obscured. In short, since the explanations in other texts are almost the same as the Abhidharma works, there is no need to explain them there.
Now then, how is it that sluggishness which operates as a proximate factor of instability and discursiveness which operates as a variable are considered to be one? In the same way, how is it that ebullience which operates as a proximate factor of instability and discursiveness which acts as a variable are considered to be one? Sluggishness, drowsiness are not the same. Sluggishness is a part of bewilderment-erring. Drowsiness can be either positively or negtively toned; hence, sluggishness is said to be a proximate factor of instability and drowsiness is said to be a variable. In the same way, with regard to ebullience and worry, ebullience is part of passion-lust. Worry can be either positively or negatively toned; hence, ebullience is said to be a proximate factor of instability and worry is said to be a variable. They are considered as one in the scheme of the five obstructions and said to be one insofar as they start from the same cause, are extinguished by the same antidote, and are identical in their function.
That they occur from the same cause means that both sluggishness and drowsiness start from over-stuffing oneself with food, from an unhappy mind, from a fainthearted attitude, and from relishing things. Both ebullience and worry start from indulging in the pleasures of the senses, playing around, laughing, and believing the fiction that one will not die.
That they are extinguished by the same antidote means that both sluggishness and drowsiness are overcome by an awareness of light, andebullience and worry are overcome by holding the mind to an inner object (idea).
That they agree as to their function means that they agree because sluggishness
and drowsiness make the mind withdraw inward and thus they obstruct concentration.
Even worse, they obstruct lucidity of ideas and so they prevent the mind
from being completely concentrated.