A lot of work was done in the philosophy of science at the beginning of the 20th century because physics had pushed so far into the frontiers of theoretical explanation that normal ways of thinking had to be set aside. For example, it became theoretically acceptable to consider light as being both a wave and a particle. And Einstein's relativity theory changed the meaning of space and time. Then came quantum physics and the interpretation of it which stated that particles do not have a specific location until you measure them. Traditional questions about reality such as whether there is an underlying order were hotly debated. And very technical questions were raised about the meaning and precision of scientific terms. Is a voltmeter reading a sensory observation or a theoretical interpretation? What does the reliability of science rest on?

Some of the questions raised are:

• What is the difference between science and pseudoscience?
• Is scientific knowledge an objective form of knowledge?
• Are there laws in nature?
• How does scientific explanation work?
• What is the difference between induction and prediction?
• Can biology be reduced to chemistry?

EXPLANATION IN SCIENCE

The philosopher Carl Hempel (1905-1997) proposed what is called the "deductive-nomological" model of explanation in 1948. An explanation is similar in form to a deductively valid argument. The premises must contain a scientific law, and the conclusion is a description of the event that is being explained. Hempel also believed that this form was the same for a scientific prediction. Philosophers of science after Hempel have criticized his model for a number of reasons. In 1962 Hempel described a second form of scientific explanation called the "inductive-statistical" model. In this model the premises provide some probability for the event being explained. The premises must contain a statistical law.

OBJECTIVITY IN SCIENCE

In 1962 Thomas Kuhn (1922-1996) wrote a book entitled "The Structure of Scientific Revolutions" in which he stated that scientists work in a system which he called "normal science". In normal science, the theories are accepted without question, and most research is intent on finding different applications for the accepted theory. The theoretical system is a "paradigm" which everyone assumes is true. After a while some problems arise in trying to apply the paradigm, but this does not shake the confidence in the theory. Only when a significant number of problems pile up does a "revolution" occur. In this revolution the entire paradigm or theoretical system is discarded and a new paradigm or theoretical system is brought in. Everything must now be interpreted in light of the new paradigm. Then this new paradigm become the "normal science" and everyone assumes it is true. Kuhn's philosophy was quite different from the previous approach which stated that science made progress by gradually building on previous work. Kuhn's philosophy stated that it was a revolutionary, not a gradual approach which scientific development used.

THE PROBLEM OF INDUCTION

To put the problem very simply, how do we know the future will be like the past? Since scientific principles are universally stated, on what basis do we believe that they will hold in the future? Or in other places? How do we know the laws of chemistry are the same in other galaxies as they are in our galaxy? Philosophers such as Aristotle (384-322 B.C. ) and David Hume (1711-1776) have wrestled with the problem of induction. One position is called the "hypothetico-deductive" model. A hypothesis is generated through a psychological process of discovery and consequences are deduced from it to provide an explanation. The strength of the justification of the hypothesis is determined by how much inductive support there is for the hypothesis. One philosopher, Karl Popper (1902-1994) , feels that in science there is no inductive support for a hypothesis. What scientists try to do is falsify the hypothesis. The problem of induction in science has now become the problem of confirmation. What are the standards or criteria which determine how much the evidence confirms a hypothesis?

PHILOSOPHY OF BIOLOGY

There is a branch of the philosophy of science which deals with questions that arise in biology:

• What is the logical structure of the theory of evolution?
• Can biology (life) be reduced to chemistry?
• How do you define the function of a biological component?

PHILOSOPHY OF CHEMISTRY

The main question in this part of the philosophy of science is whether chemistry can be reduced to physics. Other questions about the nature of chemical explanations are also discussed.

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