Human languages are not particularly logical systems. They are linguistic systems which, for their successful operation, depend on the innate human language faculty that we are all born with, not on logic or mathematics.
If languages were totally logical, then the past tense of the English verb go would be “goed”, not went, and the past tense of put would be “putted”, not put. “Childs” and not children would be the plural of child.
The suboptimal logic inherent in the structures of human languages is particularly clear if we look at certain types of English grammatical word-building processes.
For instance, if someone is hopeful, then they can presumably be said to be full of hope or, if not exactly full of it, then possessing some significant amount of hope. Similarly, someone who is graceful can be said to demonstrate a fair level of grace, and something which is beautiful exhibits a certain degree of beauty, even if it is not actually full of it.
But what about someone who is bashful? Clearly, they cannot be said to be “full of bash”, because there is no such word and no such quality (although there is, of course, an English verb bash, meaning “to hit”, which is totally irrelevant here).
Bashful is an adjective which means “shy, reluctant to draw attention to oneself”. The etymology of the word is not completely clear, but the element bash may be derived from the Medieval French verb esbaïr, esbahir (Modern French ébahir) “to be amazed, astonished”, although exactly how we can arrive at the form and specific sense of bash from these medieval French words is not totally clear.
There is a similar kind of problem with the adjective rueful, except that in this case we are actually able to find the noun rue in the dictionary, where it is usually labelled “regional or archaic”; rue more usually occurs as a verb meaning “to regret”, and is admittedly rather rare in our contemporary language.
Derivational patterns where one word is derived from another by the addition of a suffix, in this case –ful, tend to be less than totally logical. They are often irregular, complicated and unpredictable in terms of the meanings of their outcomes.
Pitiful does not mean “full of pity” but “full of factors that induce pity”, while grateful does not mean “full of grate”, obviously, but “full of gratitude”.
Mournful does not exactly mean “full of mourning” but rather “expressing or indicating mourning, sorrow; doleful, sad, dismal”; the word is now mainly associated with facial expressions, personal appearance, musical sounds and bird calls, or perhaps landscapes and scenery.
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Archaic
The word archaic goes back to the Ancient (and Modern) Greek word archí “beginning” and comes down via Greek arkhaios “ancient, old-fashioned, antiquated, primitive”. This is also the source for the first element of our word archaeology. The Archaeopteryx was a dinosaur that at one time was considered to be the oldest known fossilised bird, with pteryx meaning “wing, feather” in Greek.
