During its documented history Georgian has not undergone any drastic changes. Unlike the Old Greek and Modern Greek or Old Armenian and Modern Armenian,  Old Georgian and Modern Georgian are not like two different languages. Fluency in Modern Georgian is enough to read and understand the Georgian texts
form the 5th century. The main obstacle in this case rather be the script than language. One can not read Old Georgian manuscripts or inscriptions without special knowledge of the Old Georgian alphabet. However, the difference between Modern Georgian and Old Georgian scripts is not analogous to e. g. differences between the runic alphabet and modern Swedish. The three stages in development of the Georgian alphabet form a continuity and represent a history of changes of one and the same script.

The most common division of the history of the Georgian language  is to indicate three stages:

Old Georgian : 5th --11th centuries
Middle Georgian: 12th --18th centuries
New Georgian: since 19th century
(A. Shanidze)

According to another linguistic school only two stages should be mentioned:

Old Georgian: 5th -- 11th centuries
New Georgian: since 12th century
(A. Chikobava)

Both points of view agree each on the difference between the Old and non-Old stages.

The main feature making the Georgian language of the 5th--11th centuries different from the next period is the way how to form the future tense of verb. Georgian verb has a prefix, a preverb that shows the direction of the movement expressed by verb. It can also change the meaning of a verb. All preverbs could be represented both in present and future tenses in Old Georgian. It had nothing to do with the opposition : present -- future tenses. They
expressed the direction:

(Forms of conjunctive were used in order to express the future tense in Old Georgian. This and other questions connected to the tense /aspect forms of verb will be discussed in the corresponding part of the course)

Since the11th century verb form without preverbs expresses the present tense, verb with the preverb _ future tense:

According to another classification 5 stages may be identified:

 5th -- 11th centuries
12th --16th centuries
17th -- 18th centuries
19th century
20th century

(B. Jorbenadze)

According to some other authors, both linguistics and specialists in literature, it is not reasonable
to distinguish different stages in the development of Georgian because no considerable changes have occurred either in the system or in the lexical "store" of the Georgian language since it is documented, the 5th century  (by the newest investigations since 4th century.  Zurab Sarjveladze, Dzveli Kartuli ena /The Old Georgian language/, Tbilisi, The Tbilisi Pedagogical State University Press, 1997:7; Korneli Danelia, Zurab Sarjveladze, Kartuli paleograpiis sakitkhebi /The problems of the Georgian Paleography,
Tbilisi, 1997).

The Old Georgian language, in its turn, is not homogeneous. The diversity found in Old Georgian as
well as in Middle Georgian is caused by changes in time, by different dialectal influences, and also
by the style and purpose of author.

Sound changes
One change among others that occurred in the language during the period of Old Georgian is a change of the person markers in verb; Marker x x (kh) has changed by marker h  (h) and its phonetic variants:

Degree of complexity
The complexity of text often depends more on the sphere of literature and a style of author than on the age of the work. Monuments of hagiography, where the life of the martyrs is described are written with the simple and easily understandable language while philosophical-theological works are more complicated not only due to the complexith of the topic but also because of specific terminology (both borrowed and created in Georgian). Even "ordinary" words may have a special meaning in such a work. Works by Georgian theologist and philosopher Joane Petritsi (11th-12th centuries) are more difficult to understand than the hagiographic work "Martyrdom of Shushaniki" by Iakob Khucesi (5th century).