My colleague Fiona has been pondering the fact that analysis of <coincide>, <suicide> and <decide> appears to indicate a common base element <cide>. She wondered how such a base might explain the rather different meanings of the three words.


The orthography of <decide>

Fiona started her investigation by culling this preliminary information from a resource.

"to decide, determine," lit. "to cut off," from de- "off" (see de-) + caedere "to cut"

The Latin reference sources (never rely on only one source!) do confirm that the root of the base element of <decide> is the verb <caed(ere) - caes(um) whose denotation is “cut, hew, lop”.

The question then arises, how did the Latin <caed(ere)> give <cide> in <decide>? Fiona’s reference source has this explanation.

cidere, comb. form of caedere "to strike down, chop, beat, hew, fell, slay,"

The reference to the orthographically incoherent ‘combining form’ is actually an attempt to alert us to the presence of a characteristic of Latin word structure that the reference assumes that we know about: stem vowel shift in a compounding form of a verbal stem.


Stem vowel shift in Latin

The shift of <caed(ere)> to <-cid(ere)> is an example of the “stem vowel shift” that is a characteristic of the Indo-European family of languages as a whole. We have already met two aspects of this - ablaut and umlaut - in another thread on this site.

To understand stem vowel shift in Latin we need to relate it to that other characteristic of all Indo-European languages, compounding.

  • You need to know that while Latin was rich in suffixes (especially inflectional) Latin did not prefix.
  • The ancestors of such English prefixes as <sub->, <ad-> and <inter-> were actually Latin prepositions that were free elements.
  • Consequently, the Roman grammarians themselves, and all Latin grammarians since, classify such verbs as <sub + scrib(ere)>, <ad + orn(are)> and <inter + mitt(ere)> as compounds.

While the full Latin compounding patterns are quite complex, this is what generally happened in the compounding that concerns us here: {preposition} + {verb}.

  1. The first component (preposition) attaches directly to the second component (with assimilation if appropriate - Kit 6 Theme B in your Tool Box).
  2. If the stem vowel of the second component (verb) was <a> or <ae> it shifted to <i> or, less frequently <e>.

So - since the stem vowel of <caed(ere)> is <ae>, it shifts to <i> in a compound, giving <-cid(ere)>.

<de + caed(ere) → decid(ere)>

Voilà! We have the root of our <decide>. The metaphor behind the lexicographic denotation of “decide’ is of resolving difficulties "at a stroke (as if cutting a knot)."


The bound English base <cide> “kill”

Fiona had included <suicide> in her initial evidence bank. The bound base <cide> in this word is referring to killing, a sense that is easily associated with the idea “cutting / striking down” present in the Latin <caed(ere)>. The base <cide> with this sense of “killing” is present in several Latin compounds.

<fratricide>    <homicide>    <infanticide>    <regicide>
<herbicide>    <pesticide>    <insecticide>    <matricide>
<fungicide>    <deicide>       <vermicide>     <parricide>


Making sense of <coincide>

So what, wondered Fiona, has this to do with <coincide>? She thought that she could see the a link between “killing” and “falling”.

“If you move from kill to fall down or strike down then you are doing it together”.

Fiona again visited her reference for confirmation and found this.

coincide : 1715, from Fr. coincider (14c.), from M.L. coincidere (in astrological use), lit. "to fall upon together," from L. com- "together" (see co-) + incidere "to fall upon" (in- "upon + cadere "to fall;"

A careful reading of this evidence, however, now reveals that we are dealing with entirely distinct Latin verbs!

- The root of the bound base spelled <cide> in <coincide> is <cAd(ere)>,  but the root of the base also spelled <cide> in <suicide> and <decide> is <cAEd(ere).

- The stem vowel shift of both <caed(ere)> and <cad(ere)> gives the identical result <-cid(ere)> for both.

So the spelling similarity of the bound bases of <coincide> and <decide> turns out to be coincidental!


Further examples of stem vowel shift in a Latin root

Fiona’s orthographic musings, then, helpfully remind us of two important imperatives in word study:

  • we must always look further than surface features of written words;
  • rigorous orthographic etymology is an essential component of word study.


Here, for your further study, are examples in which the shift goes to both <i> and <e> in the same verb.

The Latin root < fac(ere) / fact(um) > "make, do, cause" shifts to <-fic(ere) / -fect(um) > in compounds.

<facile> <difficulty>        <factor> <affect>


The Latin root < cap(ere) / capt(um) > “take, hold, seize” shifts to <-cip(ere) / -cept(um) in compounds.

<capacity> <percipient>      <capture> < receptive>

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