Etymology
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constructive (adj.)

1670s, "derived by interpretation, not directly expressed but inferred," from French constructif or directly from Medieval Latin constructivus, from Latin construct-, past-participle stem of construere "to heap up," from assimilated form of com "with, together" (see con-) + struere "to pile up" (from PIE root *stere- "to spread").

Meaning "pertaining to construction" is from 1817; sense of "having the quality of constructing" is from 1841, especially "contributing helpfully." Related: Constructively; constructiveness. Constructive criticism is attested by 1841, originally in theology and philosophy.

Constructive criticism has frequently secured, in various departments of scientific inquiry, positive results, the value of which cannot be over-estimated; but there are not wanting instances in which a destructively critical method has performed services equally as valuable. Groundless hypotheses, unwarrantable theories, and baseless prejudices, required to be swept away, so that a constructive criticism might operate freely and successfully. [The Christian Ambassador, vol. ix, 1871]

It later was extended to education and became personal:

Constructive criticism points out a specific deficiency, and suggests a specific remedy. It is destructive in tearing down the wrong, but constructive in replacing value. Such criticism will afford the teacher the satisfaction of having a definite basis on which to work. [George M. Baker, "Constructive Supervision," in The American School Board Journal, February 1918] 
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poet (n.)
Origin and meaning of poet

"one endowed with the gift and power of imaginative invention and creation, attended by corresponding eloquence of expression, commonly but not necessarily in a metrical form" [Century Dictionary, 1895], early 14c., "a poet, an author of metrical compositions; one skilled in the art of making poetry; a singer" (c. 1200 as a surname), from Old French poete (12c., Modern French poète) and directly from Latin poeta "a poet," from Greek poētēs "maker, author, poet," variant of poiētēs, from poein, poiein "to make, create, compose," from PIE *kwoiwo- "making," from root *kwei- "to pile up, build, make" (source also of Sanskrit cinoti "heaping up, piling up," Old Church Slavonic činu "act, deed, order").

Replaced Old English scop (which survives in scoff). Used in 14c., as in classical languages, for all sorts of writers or composers of works of literature. Poète maudit, "a poet insufficiently appreciated by his contemporaries," literally "cursed poet," is attested by 1930, from French (1884, Verlaine). For poet laureate see laureate.

"Communication" will not explain poetry. I will not say that there is not always some varying degree of communication in poetry, or that poetry could exist without any communication taking place. There is room for very great individual variation in the motives of equally good individual poets; and we have the assurance of Coleridge, with the approval of Mr. Housman, that "poetry gives most pleasure when only generally and not perfectly understood." [T.S. Eliot, "The Use of Poetry and the Use of Criticism"]
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