A lot of things that try to pass themselves off as science, like homeopathy, clearly aren't scientific. But it might surprise you to know that there's no simple checklist or flow chart that lets you separate the scientific from the nice-try-but-not-quites. It's not for lack of trying; for decades, philosophers worked to figure out how a decidedly human activity could produce such reliable information, but all the big-name thinkers in the field have come up short.

Understanding why they failed is the subject of multiple graduate-level seminar classes. But if you're just interested in a brief overview, Tim Lewens can help you out.

Dr. Lewens is a philosopher of science at Cambridge University (and a Ford driver, as we discover) who's written a book called The Meaning of Science (UK). It's meant for a general audience, yet it tackles hairy issues in the philosophy of science and throws in ruminations on the nature of humanity for free. The Meaning of Science is an odd mix that doesn't quite hang together as a coherent whole, but it's not a bad read for anyone interested in a quick-and-painless introduction to the mystery of why science works.

The philosophy of natural philosophy

Science was once called natural philosophy, but the two largely went their separate ways for centuries. It was only last century that philosophers seemed to realize that science was doing interesting things, and it was probably worth understanding why science was so productive (a question also tackled by historians and sociologists). Lewens devotes time to the two biggest names who took up the challenge: Karl Popper and Thomas Kuhn.

In Lewens' telling, Popper took his cues from the godfather of empiricism, David Hume. In Popper's view, Hume conclusively demonstrated that inductive reasoning is unreliable. Since science is reliable, it must not involve induction. Popper felt that he had constructed a viable alternative based on falsification, i.e., the art of showing that something cannot possibly be right. The ability to show that something is wrong is an important part of science. Yet at the same time, scientists induct constantly.

There's probably a near-infinite number of ideas that we haven't looked at in enough detail to know they're wrong. Yet scientists favor specific models precisely because they can interpret evidence as favoring some ideas and not others. Besides, lots of ideas that were clearly wrong—they were falsified—turned out, when tweaked slightly, to produce valuable theories. Gregor Mendel's laws are violated all the time, but the violations can be accounted for and tell us plenty about biology.

Instead of exploring the nature of scientific evidence, Thomas Kuhn's Structure of Scientific Revolutions focused on how it's produced. Kuhn posited that explanatory paradigms direct research until they are overthrown in a revolution to make way for new paradigms. While the concept of a paradigm is pretty accurate—cosmology clearly operates under a Big Bang paradigm—the whole revolution thing isn't. Again, think of Mendel, whose ideas took us from pre-evolutionary biology up through the discovery of DNA's structure and beyond, all without a hint of revolution.

Lewens also devotes a chapter to the question of what qualifies as science. He covers familiar ground—intelligent design isn't science, while treating someone with homeopathy can be scientific, since it triggers a placebo effect. But each case is reasoned through individually, and Lewens enunciates no clear set of standards to demarcate the border between science and other stuff—though to be fair to him, nobody else has come up with one either.

Another fun section of The Meaning of Science evaluates the notion that we know science is working because its theories are so successful at predicting future behavior. Lewens correctly points out that we don't have any sense of how many wrong theories could be equally successful, so it's premature to declare victory.

Science talks back

Science isn't just a subject of philosophical rumination; scientific discoveries inform a lot of philosophical debates, and Lewens makes that the focus of the second half of the book. For example, as biologists tease apart the interactions between genetics and the environment, their work can inform the perpetual debate about the relative roles of nature and nurture. The state of that debate influences what we think about human identity, which in turn influences the sorts of genetic manipulations we're willing to tolerate. Lewens looks at a number of examples like these, as well as how science has informed our understanding of free will and altruism.

This seems to be the weaker part of the book, as it's not clear that the topics examined here cover the full range of intellectual thought. Physics and cosmology, which tell us some very strange things about the nature of the reality we find ourselves in, don't show up at all, even though they're the subject of a lot of consideration by a very active community of philosophers. The subjects that are considered feel like a scattershot sampling that's focused on biology.

In several cases, Lewens describes the ideas of people who disagree with him, then discusses why he doesn't find their arguments persuasive. The problem with this approach is that his intellectual opponents have undoubtedly also heard Lewens' arguments and don't find them to be persuasive. When Lewens doesn't explain why that's the case, it feels like listening to half a discussion.

That's not to say that there isn't thought-provoking material in these chapters. For example, Lewens notes that both genetics and the environment contribute to success in school. He goes on to describe how some policymakers have concluded that it should be considered a success if we got schools to the point where genetics started playing a larger role, as it could imply that we have gotten the environment to be less of a hindrance to students.

In a lot of ways, the two sections of The Meaning of Science are best read separately. The first section is best understood as an introductory overview to the philosophy of science that covers how ideas build on one another over time. (Lewens includes a "further reading" list at the end of each chapter, so following up on a topic or a thinker is simple.) The second section is best read with each chapter viewed as an item on an a-la-carte menu. Ideas don't really build on each other, and if a chapter doesn't interest you, you can just skip ahead to one that does. You can decide for yourself whether it's worth buying a book knowing you might not read all the chapters.

Throughout The Meaning of Science, Lewens's writing is clear, approachable, and sprinkled with relevant, current examples (like how his debate over buying that Ford tells us something about free will). But for both sections, it's Lewens' annotated further reading lists make the book truly worthwhile for readers who want more after his introduction.