Object of investigation,to the levels of language hierarchy and to two plans of the language

 
In 
the 17
th
 century French scholars Arnauld A. and Lanselot C. wrote their 
Universal or Rational Grammar of the Port-Royal concerning many Germanic 
languages. They compared phonetic, grammatical and logical categories which 
used to be the basis for creating grammar of different languages. Port-Royal 
Grammar is of great importance in linguisics, because it was the first work 
concerning language universals. 
 
The real language universals were produced in 1961 in the World Congress 
of Linguists by the group of American scholars such as John Greenberg, Lyle 
Jenkins and Charles Osgood. 
 
The problem of universals is connected with the process of unification of 
language facts and with elaboration of specific methods of discovering linguistic 
universals. Some scholars think that creation of full list of linguistic universals is 
the main task of linguistic typology. They may be of different types: synchronic and 
diachronic, absolute and statistic (полные, неполные ), deductive - inductive, 
simple and complex, universals of languages and of speech. They may be also 
attached to the levels of language hierarchy. 
Universals can be represented in the traditional way with the help of words or with 
special symbols. For example: 
1. If languages possess prepositions, they possess prefixes either. If they don't have 
prepositions, they lack prefixes. For example, the English and Russian languages 
have prepositions and they have prefixes either. Uzbek and other Turkic languages 
don't have prefixes, but these languages have postpositions. 

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2. If languages possess dual number, they possess plural number either. For 
example, in old English pronouns had singular, plural and dual numbers, but in 
modern English there exist only: singular and plural. Dual number existed in 
Sanskrit, Greek and ancient Russian.