1. Science is limited to the study of the natural world and cannot investigate “supernatural” or “metaphysical” events or causes. Science can only describe the natural world through the functioning of natural processes.  This is not to say that supernatural events or omnipotent beings may not exist, just that science cannot comment on them.
2. Scientific knowledge is limited to being inherently uncertain.
   No scientific explanation or observation is eternal or infallible. It is impossible to know that we have considered every possible explanation or that we have accounted for every possible variable.
3. Absolute "scientific truth" does not exist. This does not mean that scientific ideas should not be accepted because they "cannot be proven." All scientific knowledge is tentative and subject to revision and modification with the introduction of new evidence.  We only have our current explanations. We cannot be sure that someone in the future will not come up with something better.

1. We assume that the world is real. The physical universe really does exist as we perceive it to. In other words, it is not just a figment of our imagination.
2. We assume that natural processes are sufficient to explain the natural world. Whether they truly are sufficient is clearly unknowable, but in order for science to function productively, we assume that there is always a natural explanation for natural events.
3. We assume that humans can accurately perceive and understand the physical universe. In order for science to continue to advance, we must assume that such understanding is possible.
4. We assume that nature operates the same way everywhere in the universe, and at all times, except where we have contrary evidence. This is sometimes called the "principle of uniformity."

It turns out that the limitations are actually one of the strengths of science.  Because scientific explanations are always open to revision as new evidence is uncovered, they can continue to improve and their usefulness will continue to increase.

Science does not, however, assume "philosophical naturalism. " Rather, science leads to "methodological naturalism" if one takes it as one’s preferred method of answering questions about the world.  In other words, scientists study what they can using the methods they have at their disposal.  It is important to note that there are certainly other valid methods of answering questions about the world.

One other important characteristic of scientific explanations is that they must be capable of being disproved. Because supernatural events or causes cannot be consistently observed, they can never be disproved and so cannot qualify as scientific explanations.

Science is therefore limited to the study of the natural world and cannot study or explain "supernatural" events or omnipotent beings.  This does not mean that science is inherently atheistic or that scientists are not allowed to personally believe that the supernatural realm exists.  As one philosopher noted: science is no more atheistic than plumbing.

One thing that sets science apart from other ways of knowing is that it attempts to be self-correcting. Current scientific knowledge and understanding is subject to regular review and re-analysis. Experimental results require independent duplication and confirmation by other scientists to obtain acceptance.  Scientific knowledge is made available for public scrutiny and analysis to anyone who wants it.

The real “scientific method” is critical thinking. Critical thinking acts as the "filter of science." Scientists use comparative critical thinking to determine which explanations are more likely to be correct when compared to the alternatives. There are several criteria scientists use when deciding among alternatives. Some of these criteria are consistency, reliability, predictive power, simplicity, and generative power. By thinking critically about our scientific explanations, we can reduce the degree of uncertainty in our scientific knowledge.

In a democratic society like our own, it is often argued that out of "fairness" all viewpoints should be addressed, regardless of their consistency with actual scientific evidence. This type of thinking goes against the entire principle of comparative critical thinking that makes science such a reliable way of knowing.

Fortunately, science is not a democracy. Not every explanation is equal when we use comparative critical thinking. Scientific explanations are constantly checked against the evidence they purport to explain. Only those explanations that stand up to the scrutiny of the scientific community are provisionally accepted.

The other problem with this question is that it incorrectly refers to "alternative theories" as though they have achieved the same level of support as actual scientific theories. In general, scientific fields like Biology, Physics, or Chemistry have very few comprehensive theories that tie together the related observations and hypotheses within that field. As it turns out, there are usually no suitable "alternatives" once an idea has achieved the designation of "theory." When "alternative theories" do come about, they cause major shifts in scientific thinking (such as Einstein's theory of general relativity, Darwin's theories of evolution, or Margulis's Serial Endosymbiosis Theory of Eukaryotic Evolution).

Nevertheless, now more than ever, Americans must be able to make informed decisions that involve determining the value of knowledge created by science.  This is especially important as our technology continues to advance and new scientific discoveries lead to new understandings of ourselves and the world around us.

The current controversies surrounding stem cells and human cloning provide evidence of how new scientific knowledge can influence our everyday lives by making possible new medical treatments. The decision about whether to use these treatments must be informed by, but not solely based on, scientific knowledge. In other words, students must know that science is only one of many methods of answering questions. In order for new scientific knowledge to be analyzed and used appropriately, our students must leave school with a solid understanding of the nature of science.

For example, in August, 1999 the Kansas State Board of Education voted to reduce emphasis on evolution, the big bang, and other important geological ideas related to the age of the earth in the state science standards. The rationale provided by certain board members was that local school boards should have the right to decide whether students in their districts should learn about these "controversial" subjects. Some supporters of the Board hailed this decision as a "victory for academic freedom."  However, the Board members' justification was soon brought into question by the revelation that a Young Earth Creationist organization had a significant influence on language of the final draft of the standards.  For a more thorough analysis of this situation, see Jack Krebs' description here.

In addition, the Board also changed the definition of science from "seeking natural explanations for what we observe in the world around us" to "seeking logical explanations." To someone unfamiliar with science, this simple word replacement may seem innocuous. However, the change is actually very serious because it shows a complete disregard for one of the foundational limitations of science (see Question 5).  This "minor" change was intended to open the door for supernatural causes to be presented as scientific explanations.

This situation has since been resolved thanks to the wisdom of Kansas voters. But if Kansans (six of them in particular) had better understood the nature of science, this embarrassing controversy may have been avoided, or at least the public reaction may have been less divisive.  Unfortunately, the state science standards controversy appears to be brewing again. Check out Jack Krebs' public presentation concerning this issue at www.kcfs.org.

The DRAFT standards for science teacher education state that teachers of science should "engage students in activities defining the value, beliefs, and assumptions inherent to the creation of scientific knowledge within the scientific community" and "compare and contrast science with other ways of knowing."

To achieve these goals, the following abilities must be emphasized:

• Science teachers must be able to recognize and correct common misconceptions about the nature of science. These misconceptions are often deeply rooted, so simply talking about them is generally not enough.  Students must be actively involved in scientific investigations that have them experiencing what it is like to actually "do science." For instance, only when students feel the frustration associated with not having definite answers can they truly begin to appreciate the uncertainty associated with scientific explanations.
• Science teachers must consistently use scientific terms like "theory" and "fact" correctly.  These everyday words have specific meanings in science.  For instance, in everyday language, "theory" often refers to someone's guess, hunch, or personal opinion. A "scientific theory" is an integrated, comprehensive explanation of many scientific observations capable of generating additional hypotheses and predictions about the natural world. When someone says, “I have a theory about that," either he or she is on the brink of an incredible scientific advance, or he or she is using the scientific term incorrectly. To avoid confusion, science teachers must be careful to use these words correctly and, whenever possible, insist that their students use them correctly too.
• To avoid misunderstandings about the "scientific method," science teachers at all levels should not teach that all scientific investigations must follow a predefined sequence of steps.  Instead, the use of inquiry and critical thinking activities should help students to independently explore the methods of science and come to realize its creative and productive qualities.
• Rather than limiting coverage of the nature of science to one or two lessons at the beginning of the year, science teachers should try to incorporate the topic into their lessons throughout the year.  This can be done by simply reviewing the definitions of "theory" and "hypothesis" or by discussing the societal impacts of current events in science, etc.
• Science teachers must be careful when using certain words that are inappropriately associated with science because they can influence students’ understanding of the nature of science.  "Proof" is one such word. This word refers to knowledge or ideas that are indisputable and cannot be challenged. Scientific knowledge is based on available evidence that must be evaluated and assessed and is therefore open to multiple interpretations. The word "evidence" could be used instead. The word "believe" is another word to be used sparingly in the science classroom. One definition of "believe" is "to have faith, especially religious faith."  The unintended implications of using the word "believe" in science are obvious. Lastly, science teachers should be careful not to refer to “scientific authority.” While “expertise” is highly regarded in science, there is no rule that scientists must concede to the ideas of an absolute authority.