Rationale
The expansive movements of science, technology, trade, diplomacy, and the arts, combined with the historical dominance of the Greek and Latin languages have resulted in a large common vocabulary among European languages. With Interlingua an objective procedure is used to extract and standardize the most widespread word or words for a concept found in a set of control languages: English, French, Italian, Spanish and Portuguese, with German and Russian as secondary references. Words from any language are eligible for inclusion, so long as their internationality is shown by their presence in these control languages. Hence, Interlingua includes such diverse word forms as Japanese geisha and samurai, Arabic califa, Aboriginal kanguru, and Finnish sauna.
Interlingua combines this pre-existing vocabulary with a minimal grammar based on the control languages. People with a good knowledge of a Romance language, or a smattering of a Romance language plus a good knowledge of the international scientific vocabulary can frequently understand it immediately on reading or hearing it. Educated speakers of English also enjoy this easy comprehension. The immediate comprehension of Interlingua, in turn, makes it unusually easy to learn. Speakers of other languages can also learn to speak and write Interlingua in a short time, thanks to its simple grammar and regular word formation using a small number of roots and affixes.
Once learned, Interlingua can be used to learn other related languages quickly and easily, and in some studies, even to understand them immediately. Research with Swedish students has shown that, after learning Interlingua, they can translate elementary texts from Italian, Portuguese, and Spanish. In one 1974 study, an Interlingua class translated a Spanish text that students who had taken 150 hours of Spanish found too difficult to understand. Gopsill has suggested that Interlingua's freedom from irregularities allowed the students to grasp the mechanisms of language quickly.
Words in Interlingua retain their original form from the source language; they are altered as little as possible to fit Interlingua's phonotactics. Each word retains its original spelling, pronunciation, and meanings. For this reason, Interlingua is frequently termed a naturalistic IAL. (The term "naturalistic" is used in another sense with respect to artistic languages; in this sense Interlingua is not naturalistic.)
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