Ii. Basic concepts of contrastive linguistics

Substantial and non- substantial scientific comparison
Typology as a method of scientific study is characteristic to many fields of scientific knowledge because the taxonomic description, classification and systemiccomparison of various objects are universal methods of cognition and apply to both nonlinguistic and linguistic sciences. Taxonomy is a science studying theory of clas­sification and systemizing.
Basic types of scientific comparison
There are 2 types of scientific comparison:
a) substantial
b) non- substantial.
Substantial comparison deals with comparison of real objects materializing 
substances, e.g. sounds, digits, numbers, etc.
Non-substantial comparison deals with comparison of systems and their
ele­ments (e.g. phonemes, morphemes).
At the early stages of development of typology as a science the major role belonged to substantial comparison which is considered primary. Yuri Rojdenstvenskiy' wrote that "...in General linguistics the relations between language systems base on substantial features. The languages were considered cognate because the linguistsfound principal similarity in their substance: sound and content".
Non-substantial comparison played a significant role in shaping typology as
an independent science.
Internal and external approach
There are two approaches to language description: internal and external.
Internal approach deals with the comparison of the systems of any concrete language. It is inner comparison within one concrete language. External approach deals with thecross-language comparison.
Contrastive linguistics may compare language systems panchronically though they are living or dead; besides, it may compare language systems synchronicallyand diachronically.
The diachronic approachis a stative study of a certain period. The synchronic approach is a dynamic one.