In Answer To Abdul's Comment About Colons

Here is what The Chicago Manual of Style has to say about the colon: 

You can use a colon to relate clauses and introduce statements, quotations, or lists. 

Relating Colons: 

The colon is used to mark a break in grammatical construction equivalent to that marked by a semicolon, but the colon emphasizes the content relation between the separated elements. The colon is used, for example, to indicate a sequence in thought between two clauses (shows that they are related) that form a single sentence or to separate one clause from a second clause that contains an illustration or amplification from the first.   

Here are the sentence examples from the book: 

• The officials had been in conference most of the night: this may account for their surly treatment of the reporters the next morning. 
• Many of the policemen held additional jobs: thirteen of them, for example, doubled as cabdrivers. 

In the first sentence the colon separates the two independent clauses. The first clause is a complete sentence with a subject: "The officials," and the verb: "had been." The second clause is also complete with the subject: "their," and verb: "treatment." These clauses are connected by "this," which points back to the experience of the officials, that they were in a conference most of the night. So that connection is emphasized by the use of the colon instead of a semicolon. 

In a similar way in the second sentence the is complete with a subject: "policemen," and verb: "held." The second is also complete with a subject: "Thirteen," and verb: "doubled." They are connected or related because the thirteen refers back to the number of policemen who hold an additional job as a cabdriver. 

If you chose to use a semicolon instead of a colon in these examples, you can, or you can separate these into two sentences. It is up to you which style you are most comfortable with, just make sure to be consistent. 

Abdul was using the colon in the sense that it can precede a list (and a list can be two or more things separated by a comma). His use of the colon would have been correct if he did not add the correlating conjunction "both": 

           On the other hand, they [words] depend  on the mind of both: speaker and listener, writer and reader. (Abdul's sentence.)

This is what the Chicago Manual of Style has to say about the colon that introduces a list or a series: 

A colon is commonly used to introduce a list or a series. If the list or series is introduced by an expression such as namely, for instance, for example, or that is, a colon should not be used unless the series consists of one or more grammatically complete clauses. If the second clause in Abdul's sentence had been an independent clause (a complete sentence with subject and predicate), and not a fragment, then the colon might have worked. 

Hope this helps! 

Here is a Youtube with some additional information on how to use a colon.