Author: Michael Zerella
Category: Philosophy of Science
Word Count: 1000
This essay will present the main reasons that scientists and philosophers of science have considered laws of nature to be an integral part of scientific knowledge. It will go on to discuss some difficulties associated with the practical application of laws of nature, and will conclude with a brief description of the contemporary debate over whether laws of nature actually exist.
Securing Scientific Knowledge
Laws of nature, classic examples of which include Newton’s laws of motion and the law of conservation of energy, are exceptionless regularities and are assumed to be fundamental features of nature.1 Once we know the fundamental features of nature, we can use them to explain (or predict) all sorts of phenomena, which is what makes science so successful. As a simple example, suppose we observe a one-kilogram object accelerate at 5 m/s2 after being subjected to a 5 N force.2 If we want to know why the object accelerated in that way, we can explain it using Newton’s 2nd law of motion.
According to the Traditional View3 of science (going at least as far back as Aristotle), science is capable of supplying incontrovertible truths about nature. The only style of reasoning that philosophers believe to be capable of supplying incontrovertible truths about anything is deductive logic, and so it was assumed that scientific reasoning must follow deductive logic in order to deliver its truths about nature (e.g. Carnap, 1966; Hempel, 1962). Deductive logic usually takes the form of an argument in which a series of premises supports a conclusion in a special sort of way. That is, if the premises of a deductive argument are true, then the conclusion is guaranteed to be true. Arguments with this form are called “deductively valid.” Our example above can be converted into a deductively valid argument thusly:
- This object has a mass of 1 kg and is subjected to a force of 5 N.
- For any object, if the object is subjected to a force of X and the object’s mass is Y, then the object’s acceleration is X divided by Y.
- Therefore, this object’s acceleration is 5 m/s2.
Premise 1 describes the starting conditions, Premise 2 is Newton’s 2nd law of motion, and the conclusion is a description of the phenomenon. If both premises are true, then they guarantee that the conclusion (3) must also be true, and what better explanation for a phenomenon could we expect than a demonstration of why the phenomenon is guaranteed to happen given the initial conditions? The explanation becomes a prediction if we know the initial conditions but have not yet observed the results. By the end of the Enlightenment, repeated success in using laws of nature to explain and predict a wide variety of phenomena had popularized the notion that the universe is like a giant clockwork mechanism in which scientists, given a precise account of current conditions, could predict the exact state of the universe at any point in the future.
Of course, in order for a deductive argument to successfully guarantee the truth of its conclusion, the premises themselves must actually be true. In our example above, careful measurement can support the truth of the first premise because it is a description of a single object and event. The second premise, however, is a generalization rather than a direct observation of a single event, and normally there is no guarantee that such a generalization will continue to hold in the future. A famous example: Even the past observation of ten thousand swans, all of which are white, is no guarantee that the next swan observed will not be black. A law of nature, on the other hand, is a necessary truth about our universe rather than a mere regularity or transient pattern. Therefore, in order to ensure that both premises are true, Premise 2 must be a law of nature.
In practice, it turns out that there is a persistent mismatch between what is predicted by a law of nature and what is actually observed (see, e.g., Cartwright, 1983; Mitchell, 1997). In our example above, given the initial conditions, it is very unlikely that the acceleration of the object will turn out to be exactly 5 m/s2 because confounding factors (like air resistance or other forces) are always acting on the object, even under highly controlled conditions. In response to this problem, defenders of the Traditional View argue that if we were able to take into account every confounding factor and sum them all, we would indeed get a perfectly accurate prediction, even if this is almost never a practical possibility.
Unfortunately, the problem shows up again and becomes more pronounced when we move away from physics. In fields like geology, biology and psychology, the dynamic systems under study are highly variable and ever-changing, and so any regularities we observe are almost never universal or exceptionless. If this means that such fields do not include any actual laws of nature, then their scientific status is seriously threatened because, according to the Traditional View, real scientific knowledge is always based on laws of nature. A commonly proposed solution is to say that laws in those fields are such that they hold as long as a set of standard conditions apply, with the standards being supplied by a theory from the relevant field. Such laws are often called ceteris paribus laws4 (Schiffer, 1991).
Perhaps the most important contemporary debate in this area concerns whether nature really contains any laws at all. Critics of laws of nature (and of the Traditional View in general) use the persistent mismatch between prediction and reality described in the previous section as evidence that there are no exceptionless regularities in nature. Further, the critics argue that contemporary accounts of science deny that science aims to supply incontrovertible truths, thus undermining the need for laws of nature in the first place (e.g. Mitchell, 1997; Woodward and Hitchcock, 2003; Machamer, Darden and Craver, 2000). Proponents of laws of nature, including some who no longer follow the Traditional View, argue that even if scientific explanations and predictions do not rely on laws of nature, nature itself may still contain such laws, and nature’s laws may yet be uncovered and clarified by continued scientific investigation (e.g. Lange, 1999; Rupert, 2006).
1There are various alternative ways to characterize laws of nature. For an overview, see Hooker (1998).
2For those unfamiliar, the standard unit for acceleration (change in velocity per second) is meters per second per second, represented as (m/s)/s, or just m/s2. The unit of force is called a “Newton,” which is short for (kg ▪ m)/s2.
3There are many distinct threads running through the history of our understanding how science works. What I’m calling the “Traditional View” is just the most dominant thread.
4 “Ceteris paribus” means all else being equal or held constant.
Mike is a philosophy instructor at the University of Colorado, Boulder. Mike earned a bachelor’s degree in biology in 1993 and a master’s in biology in 1995. He then taught high school science classes for several years before going back to grad school at the University of Colorado to earn his Ph.D. in philosophy in 2011. Unsurprisingly, he specializes in philosophy of science and philosophy of biology. Mike also enjoys the classic summertime Colorado activities like hiking, biking, camping, gardening, and going to bluegrass music festivals.