Why is the cell theory considered a 'theory'?

Good question, Rachael! It is a 'theory' because there appears to be some exceptions to the rule (that we know of!) that cells are the basic structural unit of life e.g., organisms like viruses are not considered 'alive' by some because they are not 'cells', or composed of 'cells'! Also the theory as it is states that all cells arise from other cells - where did the first cell come from?. Wikipedia gives a good general explanation of cell theory, and exceptions, at:

Last edited by Steve Lolait (7th Jun 2010 07:54:05)

Hi Rachael,

Your question seems to indicate that you perhaps interpret 'theory' as meaning something about which we are unsure, or as some manner of conjecture. Whilst in colloquial usage the word 'theory' can be taken as such, in a scientific sense 'theory' has a significantly stronger sense of identity. A scientific theory, which is the sense in which it is being used in 'Cell Theory', is essentially a well-substantiated explanation of observations of the natural world. They are based on a hypothesis, or a group of hypotheses, that have been subjected to repeated testing and found to hold true (or in a more correct sense: found not to be false).

If a scientific hypothesis represents an idea that is testable by science, but which may not actually have been tested, a theory is a hypothesis that has been tested (preferably several times independently) and found to be sound, i.e. an accepted hypothesis (or indeed, group of hypotheses) that explain, and provide predictions on, a scientific phenomenon

A theory can certainly be modified to reflect new evidence, and indeed there are occasionally caveats to scientific theories, situations where they reach the extent of being useful to describe a biological phenomenon - such as the virus example Steve cites; but then this also comes down to a semantic argument as to whether viruses are in fact alive, and therefore whether they buck the trend of Cell Theory by being a smaller unit of life.

Hope that helps.

Jim, you raise some interesting points about hypotheses, theories and facts - and how different disciplines use the words. Many hypotheses in biology that are continually being tested are often called theories and have not - yet - found to be sound, and maybe should still be called hypotheses. Scientists also often use the words interchangeably. Some may argue that 'Cell theory' is more 'Cell fact' because it works in a wide variety of situations - and the 'fact' that it is a theory rather than accepted as fact (or 'Law') is a matter of tradition.

Yes, I think the use of the various terms isn't codified as well as it might be in formal biological training at degree level, that much I can testify to, certainly amongst many young biologists I meet. Those of us who cut our teeth in evo-devo forums tend to het a little het up by the lack of such distinctions.

Just as evolution is both a fact and a theory (it both being observable phenomenon, but with the mechanism of it being a theory - all be it iron clad ;-), can cell theory not be regarded in the same light? Whilst the original central tenets of cell theory are observable facts, further additions to what we consider as fundamental properties of all cells (together with the division of the extent to which such additions are true between proks and euks) means that cell theory as a term is both traditional (as you suggest), but also is probably correct.