“Our own Silent Self, helpless and witless, hidden within us, will spring forth, if we have craft to loose him to the Light, spring lustily forward with his cry of Battle, the Word of our True Wills.”
-Aleister Crowley, The Law is for All, commentary to I:7
The first question one might ask when embarking upon the quest to understand the philosophy of Thelema is “What is my Will?” or “How do I know what my Will is?” The answer to this questions might initially be presumed to be answerable in the form of a sentence such as “my Will is to be a doctor” or “my Will is to eat this sandwich,” but this is not so, for this is to restrict the Will to the trappings of language and reason. The Will is the innermost Motion of one’s being, an individual expression of the Eternal Energy of the cosmos.
“The Way that can be named is not the Eternal Way.” 
To confine the Will to logical expression is to inherently assert a limit. Further, it assumes that one must have a logical reason for acting such-and-such way, but to do so would make one “fall down into the pit called Because” to “perish with the dogs of Reason.”  As the Beast remarked, “It is ridiculous to ask a dog why it barks,”  for this is simply an expression of its nature, not determined by any kind of rational process.
“One must fulfil one’s true Nature, one must do one’s Will. To question this is to destroy confidence, and so to create an inhibition… There is no ‘reason’ why a Star should continue in its orbit. Let her rip! Every time the conscious acts, it interferes with the Subconscious, which is Hadit. It is the voice of Man, and not of a God. Any man who ‘listens to reason’ ceases to be a revolutionary.” 
Again, to express one’s Will in terms of reason is to assert a limit. This is because of the inherently dualistic nature of not only logic & reason but language & thought themselves. To do this would be to drive a cleft into one’s being, fracturing it into multiplicity.
“Thoughts are false.” 
To experience and manifest one’s pure Will, one must not act out of notions of purpose nor out of desire for some pre-formed result or outcome.  Both of these things are manifestations of the dualistic mind and restrict one unnecessarily to the trappings of logic. The Will can only be the genuine and spontaneous manifestation of one’s inmost nature, the united whole of one’s being.
Since “the word of Sin is Restriction,”  the Will is certainly not deduced from the workings of the mind which, by its very nature, asserts division & separation and therefore restriction. When we clear away the morass of morality and the over-contemplated categories of metaphysics, the Will may more easily spring forward uninhibited.
“In logic there is a trace of effort and pain; logic is self-conscious. So is ethics, which is the application of logic to the facts of life… Life is an art, and like perfect art it should be self-forgetting; there ought not to be any trace of effort or painful feeling. Life… ought to be lived as a bird flies through the air or as a fish swims in the water. As soon as there are signs of elaboration, a man is doomed, he is no more a free being. You are not living as you ought to live, you are suffering under the tyranny of circumstances; you are feeling a constract of some sort, and you lose your independence… Not to be bound by rules, but to be creating one’s own rules…”
And this last point is important because Thelema is not illogical in that it wishes reason to be entirely abolished, but rather it wishes that it be put in its rightful place, under the governance of the Will. The mind is a harsh master and a good mistress, for once one realizes that one’s Will is not amenable to the dualisms of thought, once freed from one’s earlier bonds of logic, one may again employ reason to one’s benefit in those circumstances that call for it.
“It is not the object… to look illogical for its own sake, but to make people know that logical consistency is not final, and that there is a certain transcendental statement that cannot be attained by mere intellectual cleverness… When we say ‘yes,’ we assert, and by asserting we limit ourselves. When we say ‘no,’ we deny, and to deny is exclusion. Exclusion and limitation, which after all are the same thing, murder the soul; for is it not the life of the soul that lives in perfect freedom and in perfect unity? There is no freedom or unity… in exclusion or in limitation.” 
Here – outside logical dualisms, outside notions of ethics, purpose, and metaphysics – the Will can be known. This knowledge is not that of the mind which asserts duality – a knower and a thing known – but the experiential knowledge, the gnosis, of immersion in the flow of the world. Here the Eternal Will runs through oneself, is oneself, for “…mind, never at ease, creaketh “I”. / This I persisteth not, posteth not through generations, changeth momently, finally is dead. / Therefore is man only himself when lost to himself in The Charioting.”  Therefore, one ‘knows’ one’s Will in doing one’s Will. The Will that is not restricted by mental formulations springs freely from one’s innermost Self, crowned & conquering.
“Life is fact and no explanation is necessary or pertinent. To explain is to apologize, and why should we apologize for living? To live – is that not enough? Let us then live!” 
 Lao Tsu, Tao Teh Ching, ch.1
 Liber AL vel Legis, II:27
 Aleister Crowley, The Law is For All, commentary to II:31
 Aleister Crowley, The Law is For All, commentary to II:30-31
 Aleister Crowley, The Book of Lies, ch.5
 A reference to Liber AL vel Legis, I:44, “For pure will, unassuaged of purpose, delivered from the lust of result, is every way perfect.”
 Liber AL vel Legis, I:41
 D.T. Suzuki, Intro to Zen Buddhism, p.34
 D.T. Suzuki, Intro to Zen Buddhism, p.37
 Aleister Crowley, The Book of Lies, ch.8
 D.T. Suzuki, Intro to Zen Buddhism, p.41