Key message: Scientific methods are scientifically conducted methods.
Are there rules that specify exactly how a scientist must proceed in order to gain new knowledge? Is there a simple standard for distinguishing scientific methods from unscientific ones?
“As Feyerabend … says, ‛The idea that science can, and should, be run according to fixed and universal rules is both unrealistic and pernicious‛ …
If we have a conception of science as an open-ended quest to improve our knowledge, then why cannot there be room for us to improve our methods and adapt and refine our standards in the light of what we learn." (Chalmers, A. F. (2007) What is this thing called Science. University of Queensland Press)
Every research discipline has recognized research methods that are carried out according to recognized rules. There are, however, no exhaustive lists of permissible scientific methods for each scientific discipline. If there were such lists, then methods that are not on the list should not be used in research. It would be very difficult to set up such lists, because in research often many scientists work together and use countless "auxiliary methods". Also, the "auxiliary methods" must be carried out scientifically so that the research can be successful.
"The Nobel Prize for Physics goes to the British Peter Higgs and the Belgian François Englert this year for the development of the so-called Higgs mechanism. ... Probably the experts have debated whether the European nuclear research center Cern also gets the price. Finally, in 2012, the Higgs boson was detected there - and the almost 50-year-old theory of Englert and Higgs thus only confirmed. However, selecting a single Cern experimenter and honoring the Nobel Prize for the discovery of the Higgs particle would have been difficult. Studies by CERN researchers usually have hundreds, and often thousands of authors, because they are all involved in the experiments. ... " (www.spiegel.de/wissenschaft/natur/physik-nobelpreis-2013-spaeter-triumph-fuer-higgs-und-englert-a-926775.html, 28.01.14, my translation)
If there are no lists listing all allowed research methods, does it follow that all methods are allowed? No, methods which are based on belief or which are carried out unscientifically are excluded from research. All methods that are comprehensible and correspond to current or improved scientific standards may be used.
From the above quote from Chalmers I derive this definition: Scientific methods are scientifically carried out methods. To do a method scientifically, however, is not so easy (see below). Even the best method is worthless if it is performed unscientifically.
Helmut Seiffert says in the first volume of his "Introduction to Philosophy of Science" (8th Edition 1973, Munich: Verlag C. H. Beck, pp. 79-80, my translation):
"We must therefore confine ourselves to the general requirement that scientific statements are made with the help of the "appropiate" method.84 ...
[There is] a compulsion ... to take note of the factually existing pluralism of methods. (Note 84: Kamlah, W., Logische Propädeutik oder Vorschule des vernünftigen Speens. Mannheim: Bibliographic Institute, p 118f., 124, 143)"
Conclusion: In research as well as in a the preparation of a thesis or dissertation, an attempt should first be made
to reach the goal with recognized scientific methods. Only if this is not possible should recognized methods should be modified or new (self-developed) methods should be used ("methods and
standards can be improved", see above). Every change or every new method must be comprehensibly described and explained.
How to select, modify, and develop methods, see "How to develop and apply Methods?"