• physics
• chemistry
• biology
• 1/2 geography: physical geography, geology, metereology
• 1/2 psychology
• astronomy

some other subjects, such ESS and metallurgy, draw on or combine different subject areas;

other areas, such as medicine and engineering, are applications of the sciences.

in brief:
our guess that water always boils at 100 C, while correct in New York, London, Mombasa and Dubai, turns out to be false when we try it in some other places, such as Kigali or Quito, so we have to rethink – the boiling point turns out to depend on the altitude, and is 100 C only at sea level.

in brief:
the different mortality rates in the two wards led Semmelweiss to the discovery of germs – the difference was in the schedule of the medical students training at the hospital: autopsy followed by ward round in one ward, or ward round followed by autopsy in the other.

                   observations
                         |
  ---------------------->|
 |                       |
 |                     + | inductive reasoning  
 |                       |
 |             hypothesis, of the form
 |             "whenever ..., ..."
 |                       |
 |                       |<----------------------
 |                       |                       |
 |                       | deductive reasoning   |
 |                       |             (logic)   |
 |                       |                       |
 |                + prediction                   |
 |                       |                       |
 |                       |                       |
  ----------------- experiment ------------------
 the outcome of                     the outcome of
 the experiment                     the experiment
 contradicts the                   agrees with the
 prediction: the                   prediction: the
 hypothesis has                     hypothesis has
 been 'falsified'                   been supported

• it is descriptive, not normative:
  our model does not tell scientists what they should be doing, rather it tells us what scientists are doing;

• the prediction is derived from the hypothesis using logic – e.g.
  “All apples fall” (= hypothesis) & “This object is an apple” ⇒ “This object will fall” (= prediction)

• if the outcome of the experiment does not agree with the prediction, it may be an auxiliary hypothesis that has been falsified – e.g.
  “this object” might rise, because it actually is a balloon and not an apple;

• contrary to what many people think, science requires creativity and imagination, especially at the points marked + in the diagram – e.g.
  • to invent an hypothesis (– as in the example of the two maternity wards), and
  • to come up with a suitable experiment;

• to be accepted as scientific knowledge, an hypothesis must be testable: an hypothesis which cannot be tested may be true, but it is not scientific – e.g.
  neither “There is a God” nor “There is no God” is a scientific claim;

• in some areas it may not be possible to perform experiments, so instead for the testing we depend on further observations – e.g.
  • in astronomy,
  • in biology, because of ethical problems;

• experiments in science must be repeatable and the hypothesis must have been subjected to testing by other scientists – that is how individual knowledge becomes shared knowledge;

• an hypothesis, or various hypotheses, may be part of a theory, and the theory may be represented in a model, which helps us to visualise the theory;
  as our confidence in a theory/model grows, we come to accept the entities postulated in it – e.g.
  the success of the atomic theory has led us to believe in electrons.

it may appear that scientific knowledge accumulates steadily, always increasing,
but there are times when in some area all of the knowledge is discarded and scientists start again;

• so periods of normal science alternate with scientific revolutions (Thomas Kuhn, 1962):

• in periods of normal science, scientists work within a paradigm:
  • the paradigm determines what answers are being looked for, and even which questions can be asked –
  • e.g. telepathy and telekinesis are not part of the present scientific paradigm;

• a scientific revolution is a paradigm shift (– the idea of a paradigm shift is used quite generally nowadays):
  • there are no agreed standards even how to decide between rival hypotheses,
  • so it is 'every man for himself';

examples of scientific revolutions:

• the phlogiston theory (that heat is a substance, with negative weight) > > kinetic theory of heat,
• Ptolemy's geocentric model of the universe > > Copernicus's heliocentric model > > modern cosmology: no centre,
• Aristotelian physics > > Newtonian physics > > Einstein's Theory of Relativity;

preceding the establishment of a paradigm in (an area of) a science may be a long pre-science:

• like a constant revolution: everyone starts for himself,
• has often involved myths, superstitions, etc. – e.g.
  • astrology > > astronomy,
  • alchemy > > chemistry,
  • creationism > > theory of evolution.

 pre-science  ---------->  normal science            -----
                    ---->  working within a paradigm      |
                   |                                      |
                   |                                      |
                   |       scientic revolution  <---------
                    -----  a paradigm shift

the reason that it appears that scientific knowledge has accumulated steadily is that after a scientific revolution, in the next period of normal science, new textbooks are written which systematically 'hide' the revolution.