Scientific thinking is based on a belief in the intelligibility of
nature, that is, upon the belief that the same cause operating
under the same conditions, will result in the same effects at any
time. As a result of this belief, scientists pursue the following goals.
1. They Observe. (What conditions seem to affect the
phenomena we are observing?) In order to determine the
causal relations of physical occurrences or phenomena,
scientists seek to identify factors that affect what they 
are studying. 
2. They Design Experiments. (When we isolate potential
causal factors, which seem to most directly cause the
phenomena, and which do not?) In scientific experiments,
the experimenter sets up the experiment so as to maintain
control over all likely causal factors being examined.
Experimenters then isolate each variable and observe its
effect on the phenomena being studied to determine which
factors are essential to the causal effect.
3. They Strive for Exact Measurement. (What are the precise
quantitative relationships between essential factors and their
effects?) Scientists seek to determine the exact quantitative
relationships between essential factors and resulting effects. 
4. They Seek to Formulate Physical Laws. (Can we state the
precise quantitative relationship in the form of a law?) The
quantitative cause-effect relationship, with its limitations
clearly specified, is known as a physical law. For example, it
is found that for a constant mass of gas, at a constant
temperature, the volume is inversely related to the pressure
applied to it; in other words, the greater the pressure the
less the volume — the greater the volume the less the pres-
sure. This relationship is constant for most gases within a
moderate range of pressure. This relationship is known as
Boyle’s Law. It is a physical law because it defines a cause-
effect relationship, but it does not explain the relationship.
5. They Study Related or Similar Phenomena. (When we 
examine many related or similar phenomena, can we 
make a generalization that covers them all?) A study of
many related or similar phenomena is typically carried out
to determine whether a generalization or hypothesis can 
be formulated that accounts for, or explains, them all. 
6. They Formulate General Hypotheses or Physical Theories. A
theoretical generalization is formulated (if one is found to
be plausible). For example, the kinetic theory of gas was
formulated to explain what is documented in Boyle’s Law.
According to this theory, gases are aggregates of discrete
molecules that incessantly fly about and collide with them-
selves and the wall of the container that holds them. The
smaller the space they are forced to occupy, the greater the
number of collisions against the surfaces of the space.
7. They Seek to Test, Modify, and Refine Hypotheses. If a
generalization is formulated, scientists test, modify, and
refine it through comprehensive study and experimentation,
extending it to all known phenomena to which it may have
any relation, restricting its use where necessary, or broaden-
ing its use in suggesting and predicting new phenomena.
8. When Possible, Scientists Seek to Establish General Physical
Laws as well as Comprehensive Physical Theories. General
physical laws and comprehensive physical theories are
broadly applicable in predicting and explaining the physical
world. The Law of Gravitation, for example, is a general
physical law. It states that every portion of matter attracts
every other portion with a force directly proportional to the
product of the two masses, and inversely proportional to
the square of the distance between the two. Darwin’s
Theory of Evolution is a comprehensive physical theory. It
holds that all species of plants and animals develop from
earlier forms by hereditary transmission of slight variations
in successive generations and that natural selection deter