An ideal language (also philosophical or a priori language)
is any constructed language that is built up out of first principles,
such as a logical language. Such languages are in contrast to ordinary
or spoken languages such as English, Italian, or Japanese (often called natural languages),
which have within them a great deal of fuzziness, overlap, vagueness,
ambiguity, multiple meanings, and indeterminacy of meaning for words and
phrases, unclarity, inherent contradiction, and difference between
intension and extension of terms—this is not necessarily a defect of
natural languages, but may indeed constitute a strength of them. But it
also means that those who want clarity and precision of language will be
unsatisfied with natural or ordinary languages and those who construct
an ideal language attempt to eliminate all such factors. An ideal
language entails a stronger claim of absolute perfection or transcendent
or even mystical truth rather than pragmatic principles. Philosophical
languages were popular in Early Modern times, partly motivated by the
goal of recovering what was thought to be the lost Adamic or Divine
language.
Overview
In a philosophical language, words are constructed from a limited set of
morphemes that are treated as "elemental" or fundamental.
"Philosophical language" is more or less synonymous with "taxonomic
language." Vocabularies of oligosynthetic languages are made of compound
words, which are coined from a small (theoretically minimal) set of
morphemes. Suzette Haden Elgin's Láadan is designed to lexicalize and
grammaticalize the concepts and distinctions important to women, based
on muted group theory. Sonja Elen Kisa's Toki Pona is based on
minimalistic simplicity, incorporating elements of Taoism.
A priori languages are constructed languages where the vocabulary is
invented directly, rather than being derived from other existing
languages (as with Esperanto or Interlingua).
Philosphical languages are almost all a priori languages, but not all a
priori languages are philosophical. For example, Tolkein's Quenya and
Sindarin, and Okrand's Klingon, are both a priori but not
philosophical—they are meant to seem like natural languages, even though
they have no relation to any natural languages.
History
Work on philosophical languages was pioneered by Francis Lodwick (A Common Writing, 1647; The Groundwork or Foundation laid (or So Intended) for the Framing of a New Perfect Language and a Universal Common Writing, 1652), Sir Thomas Urquhart (Logopandecteision, 1652), George Dalgarno (Ars signorum, 1661), and John Wilkins (Essay towards a Real Character, and a Philosophical Language, 1668). Those were systems of hierarchical classification that were intended to result in both spoken and written expression.
Gottfried Leibniz created lingua generalis in 1678, aiming to
create a lexicon of characters upon which the user might perform
calculations that would yield true propositions automatically; as a
side-effect he developed binary calculus.
These projects aimed not only to reduce or model grammar, but also to
arrange all human knowledge into "characters" or hierarchies. This idea
ultimately led to the Encyclopédie, in the Age of Enlightenment.
Leibniz and the encyclopedists realized that it is impossible to
organize human knowledge unequivocally as a tree, and so impossible to
construct an a priori language based on such a classification of concepts. Under the entry Charactère, D'Alembert critically reviewed the projects of philosophical languages of the preceding century.
After the Encyclopédie, projects for a priori languages
moved more and more to the lunatic fringe. Individual authors, typically
unaware of the history of the idea, continued to propose taxonomic
philosophical languages until the early twentieth century.
However, following the program of the logical positivists and the Vienna
Circle, especially as embodied in Ludwig Wittgenstein's Tractatus Logico-Philosophicus and some of the work of Rudolf Carnap, especially his book Der logische Aufbau der Welt, some analytic philosophers attempted to construct ideal languages for science—the program or movement was usually known as constructivism. A leading figure here was Nelson Goodman in his book The Structure of Appearance. Washington University in St. Louis philosopher Richard Rudner, following Goodman, carried on the attempt.