Saussure distinguishes between synchronic (static) linguistics and diachronic (evolutionary) linguistics. Synchronic linguistics refers to studying language at a single point in time, focusing on the relationships between elements within the system. Diachronic linguistics refers to studying language change over periods of time by comparing states separated by time. Saussure viewed language as having an inner duality manifested through the interaction of the synchronic and diachronic.

1. Central Concepts of Saussure: Synchrony vs.
Diachrony
Synchrony was proposed firstly by Saussure. He stated that language as a system of
signs can be studied as a complete system at any given point in time. Like chess, the
important part of language is how pieces move and the positions of all pieces relative to
one another. The shape of each piece is only important in that its potential can be
recognized. A synchronic relationship is one where two similar things exist at the same
time. Modern American English and British English have a synchronic relationship.
Diachrony is the change in the meaning of words over time. Diachrony is also named as
historical linguistics. For example in the way that 'magic' meant 'good' in youth culture
for a period during the 1980s (and, to a lesser extent, beyond). It is thus the study of
language in terms of how it visibly changes in usage. It is based in the dictionary
meaning of words.
A diachronic relationship is where related things exist separated by time. 12th century
English and 21st century English have a diachronic relationship.
Saussure criticized current linguistics as seeking to understand language changes but
not why it changed or what underlying factors were really changing.
He thus moved the study of language from diachronic to synchronic relationships.

2. Synchrony vs. Diachrony
In linguistics, the terms ‘synchrony’ and ‘diachrony’ refer to two different approaches in
linguistic research, with respect to the periods of time considered in the research in
question.
The synchronic approach means studying any aspect of language solely in one particular
period of time (typically the present), without taking into account other periods of time
in that language’s history. For example, studying the usage patterns of double negatives
in English (e.g. I ain’t got no money) in the early 21st century, without looking into the
usage patterns of double negatives in English prior to the 21st century. Most fields in
linguistics typically employ synchronic approaches as to not lose focus in their research.
The diachronic approach means studying any aspect of language by comparing it
between two (or more) periods of time, effectively focusing on the change and evolution
of whatever it is you’re looking at. As an example, studying the usage patterns of double
negatives in English in the 18th century and comparing it to the patterns in the 19th,
20th, and early 21st centuries to see how double negatives in English may or may not
have changed. By definition, historical linguistics typically employs diachronic
approaches.
See also: https://www.youtube.com/watch?v=B5vhq3aRNjE

3. Synchrony vs. Diachrony
Saussure distinguishes between synchronic (static) linguistics and diachronic (evolutionary) linguistics. Synchronic
linguistics is the study of language at a particular point in time. Diachronic linguistics is the study of the history or evolution
of language.
According to Saussure, diachronic change originates in the social activity of speech. Changes occur in individual patterns of
speaking before becoming more widely accepted as a part of language. Speaking is an activity which involves oral and
auditory communication between individuals. Language is the set of rules by which individuals are able to understand each
other.
Saussure says that nothing enters written language without having been tested in spoken language. Language is changed by
the rearranging and reinterpreting of its units. A unit is a segment of the spoken chain that corresponds to a particular
concept. Saussure explains that the units of language can have a synchronic or diachronic arrangement.
Saussure’s investigation of structural linguistics gives us a clear and concise presentation of the view that language can be
described in terms of structural units. He explains that this structural aspect means that language also represents a system of
values. Linguistic value can be viewed as a quality of the signified, the signifier, or the complete sign.
The linguistic value of a word (a signifier) comes from its property of standing for a concept (the signified). The value of the
signified comes from its relation to other concepts. The value of the complete sign comes from the way in which it unites the
signifier and the signified.
Thus, Saussure shows that the meaning or signification of signs is established by their relation to each other. The relation of
signs to each other forms the structure of language. Synchronic reality is found in the structure of language at a given point
in time. Diachronic reality is found in changes of language over a period of time.
Saussure views language as having an inner duality, which is manifested by the interaction of the synchronic and diachronic,
the syntagmatic and associative, the signifier and signified.

4. Synchrony vs. Diachrony
One can approach all different aspects of language, such as grammar, semantics,
syntax, phonology etc., from two different points of view:
- Diachronic linguistics (Diachrone Linguistik) studies language in its
development across time (this is what the term diachronic means) (Moessner
2001), whilst,
- synchronic linguistics (Synchrone Linguistik) tries to understand the functioning
of language at a single point of time, without reference to earlier or later stages.
As it is necessary to know how a system works at any given time before one can
hope to understand changes, the analysis of language at a single point in time, i.e.
synchronic linguistics, now usually precedes the study in terms of diachronic
linguistics."
(Paul Georg Meyer et al., Synchronic English Linguistics: An Introduction, 3rd ed.
Gunter Nar Verlag, 2005)

5. Synchrony vs. Diachrony
"A synchronic study of language is a comparison of languages
or dialects--various spoken differences of the same language--
used within some defined spatial region and during the same
period of time. Determining the regions of the United States in
which people currently say 'pop' rather than 'soda' and 'idea'
rather than 'idear' are examples of the types of inquiries
pertinent to a synchronic study."
(Colleen Elaine Donnelly, Linguistics for Writers. State
Univiversity of New York Press, 1994)

6. Synchrony vs. Diachrony
Saussure and Historical Linguistics
"Although nowadays one thinks of Saussure first and foremost as the
scholar who defined the notion of 'synchronic linguistics'--the study of
languages existing at a given point in time, as opposed to the historical
linguistics ('diachronic' linguistics, as Saussure called it to clarify the
contrast) which had seemed to his contemporaries the only possible
approach to the subject--in his own lifetime this was far from his main
claim to fame. . . . [A]ll his publications, and almost all his teaching,
throughout his career dealt with historical rather than with synchronic
linguistics, and indeed with detailed analysis of various Indo-European
languages rather than with the general, theoretical discourse for which
he is now famous."
(Geoffrey Sampson, Schools of Linguistics. Stanford University Press,
1980)

7. Synchrony vs. Diachrony
Language Change
"For most of the twentieth century, synchronic linguistics was considered to
be prior to diachronic linguistics. Historical linguists were expected to gather
together descriptions of a language at various points in time, relying to a
large extent on the previous work of synchronic linguists. Then they studied
the changes which had taken place by comparing the various synchronic
states. They behaved somewhat like a photographer trying to work out a
continuous sequence of events from a series of separate snapshots--on the
face of it, a sensible enough procedure. The problem was simply this:
linguists making the synchronic descriptions were, without realizing it, simply
leaving out those aspects of the description that were essential for an
understanding of language change."
(Jean Aitchison, Language Change: Progress or Decay? 3rd ed. Cambridge
University Press, 2001)

8. Synchrony vs. Diachrony
If we sum it all up, according to the method, range or scope of its study, or the focus of interest of the linguist, Linguistics can be classified into
different kinds, the chief of which are noted below: Diachronic Linguistics and Synchronic Linguistics. Diachronic linguistics is the kind in
which we study the historical development of language through different periods of time.
For example, we study how Spanish, Portugese, French and Italian have grown out of Latin. The changes that have occurred in language with
the passage of time, are also studied under this kind of linguistics; therefore, it is called historical linguistics. Synchronic linguistics is not
concerned with the historical development of language. It confines itself to the study of how a language is spoken by a specified speech
community at a particular point of time. It is also called ‘descriptive’ linguistics. Diachronic linguistics studies language change, and
synchronic linguistics studies language states without their history. According to C.F. Hockett:
“The study of how a language works at a given time, regardless of its past history or future destiny, is called descriptive or synchronic
linguistics. The study of how speech habits change as time goes by is called historical or diachronic linguistics”
The distinction synchrony and diachrony refers to the difference in treating language from different points of view. Though the historical
character of a language cannot be ignored, its present form being the result of definite historical processes, changes and transformations, it is
necessary for a complete understanding of it to concentrate on the units of its structure at the present moment. Some scholars do not see the two
approaches apart. They assert that it is a mistake to think of descriptive and historical linguistics as two separate compartments. However, on
the whole the two areas are kept apart and one is studied to the exclusion of the other. Synchronic statements make no reference to the previous
stages in the language. Linguistic studies in the nineteenth century were historical in character; they originated as part of the general historical
investigations into the origins and development of cultures and communities, especially West Asia, Egypt, etc. Such philological researches
viewed language at different stages of its progress and attempted to understand relations among different languages. Language families were
discovered and genetic affinities identified. For Zhirmunsky, Diachronic linguistics was a great discovery of the 19th century:
“Which developed so powerfully and fruitfully from the 1820s to the 1880s. This discovery enabled linguists to explain modern languages as
a result of law-governed historical development”
On a closer look one realizes that without a good synchronic (descriptive) work, valid historical (diachronic) postulations are not possible; in
other words, a good historical linguist needs to be thorough descriptive scholar too.

9. References
• http://changingminds.org/explanations/critical_theory/concepts/synchrony_
diachrony.htm
• https://www.quora.com/What-are-synchrony-and-diachrony-in-terms-of-
linguistics
• http://www.angelfire.com/md2/timewarp/saussure.html
• https://www.thoughtco.com/synchronic-linguistics-1692015
• https://neoenglish.wordpress.com/2010/12/16/write-a-note-on-linguistic-
synchrony-and-diachrony/