In science, will is a term referring to the mental faculties, operations, or surrounding circumstances connected to how one’s actions are chosen. 
Goethe | Elective Affinities
In 1809, German polymath Johann Goethe published his physical chemistry based novella Elective Affinities, wherein in the famous P1:C4 of which he compares the movements and reactions of chemicals with those of people, mentioning the term "will" in the discussion:
“I am sure you will forgive me my fault,” she said, “when I tell you what it was this moment which came over me. I heard you reading something about affinities, and I thought directly of some relations of mine, two of whom are just now occupying me a great deal. Then my attention went back to the book. I found it was not about living things at all, and I looked over to get the thread of it right again.”
“It was the comparison which led you wrong and confused you,” said Edward. “The subject is nothing but earths and minerals. But man is a true Narcissus (see: ECHO); he delights to see his own image everywhere; and he spreads himself underneath the universe, like the amalgam behind the glass.”
“Quite true,” continued the Captain. “That is the way in which he treats everything external to himself. His wisdom and his folly, his will and his caprice, he attributes alike to the animal, the plant, the elements, and the gods.”
“Man can do what he wills but he cannot will what he wills.”
— Arthur Schopenhauer (1839), On the Freedom of the Will; cited by Einstein (see: Einstein-Murphy dialogue)
“The will of the copper, claimed and preoccupied by the electrical opposition to the iron, leaves unused the opportunity that presents itself for its chemical affinity for oxygen and carbonic acid, behaves exactly as the will does in a person who abstains from an action to which he would otherwise feel moved, in order to perform another to which he is urged by a stronger motive.”
|Left: the Froude model of the will (1849), according to which the "will" of the man is "determined" as is the pull of a suspended iron rod to a stronger magnet, similar to the views Arthur Schopenhauer (1844), according to which “sin, as commonly understood, is a chimera”.  Right: a diagram showing how the will can be changed by external factors, such as the heating of the one of the magnets, during which, when reaching the Curie point (Ѻ) (or Curie temperature) (Ѻ), the larger magnet will lose its attractive power, after which the so-labeled “will” of the iron may result to be inclined, in this new system state, to the smaller magnet.|
“The source of all superstition is the fear of having offended god, the sense of something within ourselves which we call sin. Sin, in its popular and therefore most substantial sense, means the having done something to gratify ourselves which we knew, or might have known, was displeasing to god. It depends, therefore, for its essence on the doer having had the power of acting otherwise than he did. When there is no such power there is no sin.
Now let us examine this. In reflecting upon our own actions we find that they arise from the determination of our will, as we call the ultimate moral principle of action, upon some object. When we will, we will something, not nothing. Objects attract or repel the will by the appearance of something in themselves either desirable or undesirable. And in every action, if analyzed, the will is found to have been determined by the presence of the greatest degree of desirableness on the side towards which it has been determined.
It is alike self-contradictory and contrary to experience, that a man of two goods should choose the lesser, knowing it at the time to be the lesser. Observe, I say, at the time of action. We are complex, and therefore, in our natural state, inconsistent, beings, and the opinion of this hour need not be the opinion of the next. It may be different before the temptation appear; it may return to be different after the temptation is passed; the nearness or distance of objects may alter their relative magnitude, or appetite or passion may obscure the reflecting power, and give a temporary impulsive force to a particular side of our nature. But, uniformly, given a particular condition of a man's nature, and given a number of possible courses, his action is as necessarily determined into the course best corresponding to that condition, as a bar of steel suspended between two magnets is determined towards the most powerful. It may go reluctantly, for it will still feel the attraction of the weaker magnet, but it will still obey the strongest, and must obey. What we call knowing a man's character, is knowing how he will act in such and such conditions. The better we know him the more surely we can prophesy. If we know him perfectly, we are certain.
So that it appears that at the stage first removed from the action, we cannot find what we called the necessary condition of sin. It is not there; and we must look for it a step higher among the causes which determine the conditions under which the man acts. Here we find the power of motives depends on the character, or the want of character. If no character be formed, they will influence according to the temporary preponderance of this or that part of the nature; if there be formed character, on the conditions, again, which have formed it, on past habits, and therefore on past actions. Go back, therefore, upon these, and we are again in the same way referred higher and still higher, until we arrive at the first condition, the natural powers and faculties with which the man has been sent into the world.
Therefore, while we find such endless differences between the actions of different men under the same temptations, or of the same man at different times, we shall yet be unable to find any link of the chain undetermined by the action of the outward circumstance on the inner law; or any point where we can say a power lay in the individual will of choosing either of two courses—in other words, to discover sin. Actions are governed by motives. The power of motives depends on character, and character on the original faculties and the training which they have received from the men or things among which they have been bred.
Sin, therefore, as commonly understood, is a chimera.
If you ask me why, then, conscience so imperatively declares that it is real? I answer, conscience declares nothing of the kind. We are conscious simply of what we do, and of what is done to us. The judgment may come in to pass sentence; but the judgment is formed on instruction and experience, and may be as wrong in this matter as in any other: being trained in the ordinary theory of morals, it will and must judge according to it; but it does not follow that it must be right, any more than if it be trained in a particular theory of politics, and judges according to that, it must be right. Men obey an appetite under present temptation, to obey which they have before learned will be injurious to them, and which, after the indulgence, they again learn has been injurious to them; but which, at the time, they either expected would, in their case, remit its natural penalty, or else, about which, being blinded by their feelings, they never thought at all. Looking back on their past state of mind, and finding it the same as that to which they have returned when the passions have ceased to work, it seems to them that they knew better, and might have done otherwise. They wish they had. They feel they have hurt themselves, and imagine they have broken a law. It is true they have broken the higher law, but not in the way which they fancy, but by obeying the lower law, which at the time was the stronger.
Our instinct has outrun our theory in this matter; for while we still insist upon free will and sin, we make allowance for individuals who have gone wrong, on the very ground of provocation, of temptation, of bad education, of infirm character. By and by philosophy will follow, and so at last we may hope for a true theory of morals. It is curious to watch, in the history of religious beliefs, the gradual elimination of this monster of moral evil. The first state of mankind is the unreflecting state. The nature is undeveloped, looking neither before nor after; it acts on the impulse of the moment, and is troubled with no weary retrospect, nor with any notions of a remote future which present conduct can affect; and knowing neither good nor evil, better or worse, it does simply what it desires, and is happy in it. It is the state analogous to the early childhood of each of us, and is represented in the common theory of paradise—the state of innocence.
But men had to grow as we grew. Their passions developed rapidly, their minds slowly; but fast enough to allow them, in the interval of passion, to reflect upon themselves, to generalise, and form experience; and, acquiring thus rudimental notions of laws from observing the tendency of actions, men went through what is called the "fall"; and obtained that knowledge of good and evil which Schiller calls "ein Kiesen Schritt der Menscheit" ["a gravel step of humanity"]. Feeling instinctively that the laws under which they were, were not made by themselves, but that a power was round and over them greater than themselves, they formed the notion of a lawgiver [see: Critias hypothesis], whom they conceived they could please by obedience to the best they knew, and make angry by following the worse. It is an old remark, that as men are, such they paint their gods; and as in themselves the passionate, or demonic nature, long preponderated, so the gods they worshiped were demons like themselves, jealous, capricious, exacting, revengeful, the figures, which fill the old mythologies, and appear partly in the Old Testament. They feared them as they feared the powerful of their own race, and sought to propitiate them by similar offerings and services.”
See: Freud-Schiller drive theoryA variant of Schopenhauer's will to live is Austrian psychologist Sigmund Freud's 1920 death drive theory, the reverse so to speak of the former, a sort of will to death driving instinct; along with, supposedly, a "will to pleasure" theory, embodied somewhere in his 1921 Beyond the Pleasure Principle.
“The will is free. Free in what sense? It is free to act according to its nature. This, in fact is true of all realities. Take steel. Steel is free to act as steel, and nothing in existence can make steel act otherwise than steel should act.”
|Power [s] |
(of the universe)
|God[s]||"Celestial mechanics has no need of that hypothesis."||Pierre Laplace (1802)||[Ѻ]|
|"God is dead."||Friedrich Nietzsche (1883)||[Ѻ]|
|Movement||Free will||External force (80%) / internal force (20%) chemical affinity movement reaction theory||Johann Goethe (1796)||[Ѻ]|
|"A man can do what he will, but not will what he wills."||Arthur Schopenhauer (1839)|
|"will to power" drive theory||Friedrich Nietzsche (1883)|
|Retinal molecule photon mediated conformational change||Libb Thims (2007)|||
|Natural/Unnatural||Good/Evil||“I perceived something in nature (whether living or lifeless, animate or inanimate) that manifested itself only in contradictions and therefore could not be expressed in any concept, much less any word.”||Johann Goethe (1770)||[Ѻ]|
|Natural + unnatural coupling drive theory||Libb Thims (2011)|||
|Synthesis/Analysis||Life/Death||Defunct theory of life / Life terminology upgrades||Libb Thims (2009)|
|Sociology|| → deanthropomorphization of the 19th century "social matter" terminology|
Sociology terminology upgrades
|Libb Thims (2013)||[Ѻ]|
“Will is nothing more than a particular case of the general doctrine of association of ideas, and therefore a perfectly mechanical thing.”— Joseph Priestley (c.1780) (Ѻ)
“I cannot help thinking about the immediate circumstances which have brought a thing to pass, rather than about any ‘will’ setting them in motion. What is done by what is called myself is, I feel, done by something greater than myself in me.”— James Maxwell (1879), “Comment to Fenton Hort when terminally ill” 
“In conscious beings such natural tendencies are accompanied by a certain feeling which we call will, and we are happy when we are allowed to act according to these tendencies or according to our will. Now, if we recall the happiest moments of our lives, they will be found in every case to be connected with a curious loss of personality. In the happiness of love this fact will be at once discovered. And if you are enjoying intensely a work of art, a symphony of Beethoven's, for example, you find yourself relieved of the burden of personality and carried away by the stream of music as a drop is carried by a wave.”— Wilhelm Ostwald (1906), Individuality and Immortality (pgs. 44-55)
“If thought is capable of being classified with electricity, or will with chemical affinity, as a mode of motion, it seems necessary to fall at once under the second law of thermodynamics. Of all possible theories, this is likely to prove the most fatal to professors of history.”— Henry Adams (1910), A Letter to American Teachers of History