DICHOTOMY
What is dichotomy?
"Dichotomy" is a technical term, defined by Webster's New World Dictionary as meaning division into two [or more] parts. The concise way to say this, is that such things are "distinctly different" - but that immediately raises complications. No two or more things can ever be "completely contrary" because each fits into the general category of "entities". What "dichotomous" identifies, therefore, is the absence of certain features in some cases, and their presence in others. Conceivably a number of things could share a dozen features, but one half of them would possess an additional feature which the other half lacked - and on the basis of the presence or absence of that additional feature two categories might be proposed for some particular purpose.
Since things (or sets, or patterns, or structures, or situations) may display a multitude of features, the categorizing process is more credible IF the criteria for the dichotomizing is identified, and the rationale for the grouping is plausible (i.e., does it make sense, and does it [really] serve the purpose?). Referring to the presence or absence of a feature only makes sense if that feature itself has relevance to the purpose of the task at hand - categorizing on the basis of shapes or sizes, whether vastly or barely different, should not be used if these features have no bearing on what the practitioners are seeking to accomplish. However, exclusion in the absence of some variable also implies the possibility of inclusion in another category.
How does dichotomy work?
Dichotomy is most often used to "disqualify" something (in the sense that the term is used in marketing). To "disqualify" as a good prospect, a customer will lack certain characteristics: sufficient disposable income to afford the product, an intrinsic or induced need for the product, etc. During categorization, the entities that are dichotomous, as opposed to being equivalent with those being grouped according to certain features, may either be left out of consideration entirely or be placed in a category distinguished for being "without" the feature, or one possessing other features. Pose the questions: Why is this categorization necessary? and What will the grouping achieve? Problems often occur because the basis of categories is not clearly defined, nor their implications sufficiently thought through. There was a time when science (the positivistic version) was rationalized (in part) as a framework to demonstrate common features shared by many entities. All life-forms were "energy-consuming devices" and all modern habitations were "machines for living". Since the Second World War and the onset of post-modernism however, the rationale has switched to "la difference". Since every form used and every choice made excludes the other alternatives that are not engaged, differentiation can occur ad infinitum, until the distinctions made make no difference at all. One effective way to avoid this pit-fall is to recognize that homology and dichotomy are just two ends of the continuum of identity.
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