of least effort or "economy of effort". This concept has been stated as "If a word or expression remains perfectly intelligible without a certain sound, people tend to omit that sound." Historical elisions There are various ways in which the present form of a language may reflect elisions that have taken place in the past. This topic is an area of Diachronic linguistics. Such elisions may originally have been optional but have over time become obligatory (or mandatory). An example of historical elision in French that began at the phrasal level and became lexicalized is preposition > in "today", now felt by native speakers to be one word, but deriving from , literally "at the day of today" and meaning "nowadays", although is no longer recognized as meaningful in French. In English, the word "cupboard" would originally have contained /p/ between /ʌ/ and /b/, but the /p/ is believed to have disappeared from the pronunciation of the word about the fifteenth century. Contractions In many languages there is a process similar but not identical to elision, called contraction, where common words that occur frequently together form a shortened pronunciation. This may be a historical case (for example, French "ce est" has become "c'est" /sɛ/ and it would now be incorrect to say "ce est" /sə ɛ/) or one that is still optional (in English, a speaker may say "that is" /ðæt ɪz/ or "that's" /ðæts/). Contractions of both sorts are natural forms of the language used by native speakers and are often colloquial but not considered substandard. English contractions are usually vowel-less weak form words. In some cases the contracted form is not a simple matter of elision: for example, "that's" as a contraction is made not only by the elision of the /ɪ/ of "is" but also by the change of final consonant from /z/ to /s/; "won't" for "will not" requires not only the elision of the /ɒ/ of "not" but also the vowel change /ɪ/ --> /oʊ/ and in English RP "can't" and "shan't" change vowel from /æ/ of "can" and "shall" to /ɑː/ in /kɑːnt/, /ʃɑːnt/. In some languages employing the Latin alphabet, such as English, the omitted letters in a contraction are replaced by an apostrophe (e.g., isn't for is not). Written Greek marks elisions in the same way. Elision in poetry Elision is frequently found in verse. It is sometimes explicitly marked in the