The Upanishads, Part 1 (SBE01), by Max Müller, , at sacred-texts.com
1. 'Will 2 (saṅkalpa) is better than mind. For when a man wills, then he thinks in his mind, then he sends forth speech, and he sends it forth in a name. In a name the sacred hymns are contained, in the sacred hymns all sacrifices.
2. 'All these therefore (beginning with mind and
ending in sacrifice) centre in will, consist of will, abide in will. Heaven and earth willed, air and ether willed, water and fire willed. Through the will of heaven and earth &c. rain wills; through the will of rain food wills; through the will of food the vital airs will; through the will of the vital airs the sacred hymns will; through the will of the sacred hymns the sacrifices will; through the will of the sacrifices the world (as their reward) wills; through the will of the world everything wills 1. This is will. Meditate on will.
3. 'He who meditates on will as Brahman, he, being himself safe, firm, and undistressed, obtains the safe, firm, and undistressed worlds which he has willed; he is, as it were, lord and master as far as will reaches--he who meditates on will as Brahman.'
'Sir, is there something better than will?'
'Yes, there is something better than will.'
'Sir, tell it me.'
112:2 Saṅkalpa is elsewhere defined as a modification of manas. The commentator says that, like thinking, it is an activity of the inner organ. It is difficult to find any English term exactly corresponding to saṅkalpa. Rajendralal Mitra translates it by will, but it implies not only will, but at the same time conception, determination, and desire.