Laws of Motion, Capacities, and Principles
Things that are truly new do happen, but there are also some kinds of events that occur over and over. Wars between capitalist rivals have existed as long as there has been capitalism, wars that grew into enormous slaughters in the 20th century. Capitalist economic crises repeat regularly, about every eight years since 1825.
Recognizing and recording patterns and regularities like these are vital parts of scientific knowledge in any field. But seeing patterns is only the first stage of knowledge. Noticing that capitalist crises keep happening does not explain why crises happen and does not tell us whether they must happen or could be stopped somehow. But these issues are exactly what must be understood in order to know whether capitalism could be fixed or how it could be destroyed. To answer these questions we must find and use what Marx called the “laws of motion” of capitalism, which he said was his ultimate aim in his work Capital.
What are Laws of Motion?
A key feature that distinguishes a law from a mere pattern is the concept of necessity, constraint, or limitation. A law of nature exists when natural causes force things to happen according to a certain general pattern. Things that are not compatible with the law are forced not to happen. Newton’s Second Law of Motion, for example, says that a thing that moves must change speed or direction at a rate that is proportional to the force that acts on it. No other pattern of motion is possible, that is, “allowed” by nature. Modern physics tells us that it is impossible for anything to travel faster than light.
A second feature of a law is universality: a law is a pattern that always happens or never happens in a specific system and under specific conditions. What always happens might be only a tendency or statistical average, like the law of capitalism that the price of something is proportional—on the average—to the amount of labor it takes to make it. In any case, a law is a regularity that can be relied on. We will be concerned here with laws of motion, laws that determine how processes within a natural or social system operate and change over time.
The concept of a law of nature is different from a piece of legislation or the decision of a judge, but these things do have something in common. If the capitalist government makes a law, they force people to obey it by threats of jail, fines or death, even if capitalists disobey the law themselves. In physics, natural causes force or constrain the behavior of objects. The common element between laws of nature and laws made up by government is constraint or limitation. Laws of nature or economics are fundamentally different from legislation, however. In a law of nature or economics, the constraint is not imposed from the outside, but results from internal causal factors.
For example, the law of the falling rate of profit, discovered by Marx, guarantees falling profit rates unless certain kinds of counteracting factors are present. This is one of the laws of motion of the capitalist system, and it results from changes in the technology of production that are driven by competition. Nothing outside the economic relations of capitalism makes this law work, and it does not necessarily apply to other economic systems. Although this law is not imposed on the economy from the outside, its operation does compel individual capitalists to conform to it, limiting the profit they can make from a given investment.
Unlike legislation, economic and natural laws operate whether or not we can formulate them in a language. Marx wrote that in the apparently accidental events that occur in economic competition are actually carried out and regulated by inner laws. These laws only become comprehensible when many events are considered together and carefully analyzed, but laws that are not known or even expressed are still laws.
Laws and Their Expression
It is important to distinguish between a law of nature and its expression in words, which is often also called a law. A law in the most fundamental sense, however, is a necessary regularity that we can try to express in a theory. It is probably true that we never succeed completely in doing this. The lesson of history is that the expressions we call laws always turn out to be approximately true at best—nearly true but not perfectly true. They usually turn out not to be completely universal, but to be (nearly) true only for certain systems of entities. Although completely precise and universal statements of laws are probably beyond human capacity, laws are can still be known with sufficient accuracy to be an indispensible basis for much of human action.
The likelihood that laws cannot be known with complete accuracy is sometimes used as an argument that there are no laws of nature. Materialists recognize, however, that since the laws of nature do not depend on how or whether we understand them, the fact that our understanding is subject to limits is no reason to conclude that the laws we are trying to understand are not objectively real.
Laws are not the only subjects of scientific investigation. We also need to know the capacities of things, what they can do or what can be done with them. Capacities don’t always correspond to laws. If we say that aspirin cures headaches, we describe something that aspirin is capable of. We can’t say, however, that taking aspirin must cure a headache, or that it will always do so, or that it must do under specific conditions, or even that it must work in some specific portion of headaches. A capacity is something more than a possibility but can be something less than a law.
Knowledge of capacities is tremendously important for practical action. Doctors must know the capacities of various treatments in order to treat their patients. Leaders of an army must know whether their troops have the capacity to defeat a certain enemy, even if having the capacity does not guarantee victory. Knowing whether and how the working class can develop the capacity to overthrow capitalism is the central problem of Marxist politics.
Why Knowledge of Laws is Needed
As important as capacities are, however, science must aim at knowing laws. For one thing, a lack of capacity takes the form of a law. We have ample evidence that capitalism does not have the capacity to avoid economic crisis. This corresponds to a law of motion capitalism, that crises must recur regularly. No object has the capacity of travel faster than light, since it is a law that nothing can do so.
Laws also provide critical anchor points for knowledge. Newton’s three laws of motion are now known to be valid only in restricted circumstances, but determine and explain an enormous number of physical phenomena. A more general law called “Hamilton’s Principle,” which was originally derived from Newton’s laws, seems to be completely general, but this is a judgment that could change as our knowledge advances.
Notice that Hamilton’s Principle isn’t called a law, although it actually does express a fundamental law. The names that have become attached to scientific discoveries are not a good guide to whether they are laws or not. Many statements that have been called laws do not actually express laws because they aren’t true or even close to the truth.
Many laws of physics are expressed by mathematical equations that state that two combinations of quantities are equal. These are not necessarily called laws in textbooks. The Navier-Stokes equation, for example, is the most basic law of fluid mechanics, but is seldom called a law.
Kind of Laws
Laws always contain an element of necessity, but this can take different forms. Marx emphasized laws that hold for the average behavior of some economic quantity like price or profit, but which do not determine each individual case. Some laws involve a tendency that must be present, even if it can be counteracted by another tendency. The law of the falling rate of profit is this kind of law. The rate of profit does not constantly fall as capitalism develops, but capitalism has a constantly recurring tendency for the rate of profit to fall, a tendency that can be counteracted by other factors like the destruction of capital by crisis or war.
Objections to Laws
Many capitalist philosophers claim that there are no real laws in nature. There are several variations on this line (called “constructivism,” “empiricism,” etc.), but they all represent idealism. They claim that what nature seems to dictate--what makes it seem that there are necessary constraints in natural processes--is really just something that human thought puts there. These idealists recognize patterns in nature, but claim that the “must happen” character that a law requires is not really in nature itself, just in our minds. David Hume gave a classic formulation of this idea. He claimed that the necessity we find in natural regularities is a product of our own habit of expecting a certain effect to follow from its cause.
Other capitalist philosophers claim that while there are laws of nature, there can be no laws of human history, but just a series of accidents. A famous example like this is the claim that Napoleon lost his empire because of his hemorrhoids. At the battle of Waterloo, Napoleon’s hemorrhoids hurt so much that he avoided riding his horse onto the battlefield and left some early decisions to his lieutenants, who made mistakes. Those mistakes lost the battle, so the story goes, and thus the empire. A scientific analysis of the battle is very different from this, however, emphasizing superior forces that opposed the French troops.
History is not fully determined by laws, and accidental or contingent causes sometimes play an important role. When fruit seller Mohamed Bouazizi set himself on fire in January 2011, it triggered the revolt that overthrew Tunisian dictator Ben Ali and started the Arab Spring. Although oppression always provokes resistance, laws do not fully determine what form this resistance will take. Mr. Bouazizi’s action was contingent, that is, not determined by the laws of motion of politics in Tunisia.
If this “everything is an accident view” were true, it would mean that people could not make their own history, because they couldn’t learn or use laws of economics, politics or war to determine what must result from their actions or what is impossible for them to do.
Laws and Theoretical Principles
Other people object to laws because they claim that laws of nature will inevitably be confused with legislation. They prefer to talk about theoretical principles rather than laws. This is wrong in two ways. Millions of physics students have managed to understand that Newton’s laws of motion are not legislated or enforced by anyone, so the confusion is not inevitable.
Typically the “principles rather than laws” view is defended on an idealist basis. Philosopher Ronald Giere, for example, claims that we must reject laws because we can’t know general truths about “the relationship between mass, force, and acceleration.” He maintains that we can only know principles, that is, “rules devised by humans to be used in building models to represent specific aspects of the natural world.” But the fact that our knowledge of the world is imperfect is no reason to accept the idealist conception that what we take to be necessary in nature is only the necessity of our own rules for representing nature.
“Theoretical principles” certainly are not adequate substitutes for laws, since many general principles that play an important role in scientific theories are not intended to express laws. Useful principles do not necessarily describe what must happen or what is impossible. Principles can describe capacities, like "electromagnetic radiation can cause burns" or "market prices may not represent actual value."
Principles also describe calculation schemes, guides to discovery, simplifications, etc. Statements that express useful approaches to an investigation are called “heuristic principles.” A physicist, for example, may recommend to a student the principle of searching for ways in which a system is symmetrical and using that symmetry to discover simpler laws.
Scientists often appeal to methodological principles that dictate how evidence should be evaluated or how a plausible theory should be formulated, which are indispensible to the conduct of science. These principles are among those that should be rightfully called “rules devised by humans to be used in building models."  They should not be mistaken for laws of nature or social systems, since they are really principles about how to investigate a particular kind of natural or social system scientifically, not how such a system works.
The most important difference between principles and laws, however, is that there are always laws that we do not know and may never know how to express as a principle in a theory. Principles are linguistic entities, but laws don't depend on language--except, of course, laws of linguistics. A principle can only express a law that we know, and will probably express it imperfectly. Laws, however, operate whether we have discovered how to describe them or not. The inverse square law for the force of gravity that Newton discovered only became a principle when he wrote it down in the 17th century. At that time, however, this law had been effect for over 14 billion years.
In the next blog, we will explore some laws of motion of socialism.
 Ronald N. Giere, Science Without Laws, University of Chicago Press, 1999, pp. 94-95.  ibid.
May 9, 2012; modified June 7, 2012