Twain's "Corn-pone Opinions" is a fascinating, and currently very relevant essay. Selections two through four focus on some of its most important ideas.  After students read and discuss the essay, you might ask them to write an essay in which they agree or disagree with Twain's conclusions. Be sure to tell the students to include specific examples of people who do, or do not, think for themselves.

     Some students don't use semicolons; others sprinkle them over their writing like pepper on mashed potatoes. As a result, some teachers tell students not to use semicolons at all. Textbooks usually instruct students to use semicolons for two purposes: 1) to separate items in a series when those items themselves include commas (as in street addresses), and 2) to separate main clauses, especially when the main clauses express contrasting ideas. Items in a series are rare in texts, so the first rule usually does not present students with many problems; semicolons and main clauses cause headaches.
     The KISS psycholinguistic model suggests that punctuation is a reader's guide to chunking. In essence, they indicate the ends, and sometimes the beginnings, of words that chunk together into phrases, clauses, and, ultimately, main clauses. The rules that govern the use of punctuation marks developed as conventions; they were neither legislated nor set in stone. There are, as a result, two different types of problems with these rules. First, conventions change over time. In the eighteenth and early nineteenth centuries, for example, sentences tended to be longer, and semicolons tended to be used, much more frequently than they are today. How then, does one establish "rules" for conventions that do no remain constant, especially since we expect students to read texts from previous centuries? The only thing we can try to do here is to help students understand that conventional "rules" change over time.
      The second type of problem with the rules is that conventions, in order to be "taught," are often oversimplified. Writers and publishers are not legally bound to follow the rules, and some writers, especially, for example, writers of poetry, intentionally violate the rules. Thus, if they look, students will often find examples in their reading that do not fit the rules. In addition, in that they are conventions, the "rules" derive primarily from the simple cases. It is easy enough, relatively speaking, to see the contrast implicit in "He went swimming; she did the dishes." Such examples can be used to "teach" the rules. But, in real texts, sentences are not usually that simple. 
     I do not mean to suggest here that the usual textbook rules are harmful. They cannot be harmful because they are almost totally ineffective. Teaching students to use semicolons to separate main clauses means absolutely nothing to students who cannot identify the main clauses in their own writing. At worst, in other words, the usual textbook rules are simply a waste of time.
     Within a KISS-like approach, however, one needs to go beyond the usual textbook rules. We need to be honest with students, teach them how to identify clauses, teach them the basic rules, explain that these rules are conventions, and then have the students do some exploration on their own to see the extent to which these rules are valid. In rereading "Corn-pone Opinions" to select some passages for exercises for my college students, I noted that Twain used a fair number of semicolons in the essay. It could provide an interesting source of data for a study in the use of semicolons.
     There are, in my edition of the essay, forty-five semicolons. The sentences that contain them have been collected in a separate "data" document. We need to note at this point that there are probably other editions of this essay, especially when it comes to punctuation. The version used here was transcribed, years ago, from a collection of essays. Unfortunately, since the work is in public domain, I did not note the exact source. The important point here is that I did not transcribe this version specifically for this study, and I was certainly not even looking at, much less messing with, the semicolons when I made the transcription. Feel free, of course, to compare it with other versions, but as a text, this version should be an acceptable field for looking at the use of semicolons.
     Having collected the data, I examined it to explore two things -- what the semicolons syntactically separate, and the nature of the ideas that are separated.  Syntactically, I had early noted that some of the semicolons separate subordinate clauses. Thus, in looking at syntax, I attributed each semicolon to one (or more) of three categories -- main clauses, subordinate clauses, and "other." Initial observations also suggested that, in terms of meaning, some of the semicolons separate main clauses in which the second clause amplifies, rather than contrasts with, the first. As a result, for the study of meaning, the semicolons were likewise attributed to one (or more) of three categories -- those that separate contrasting ideas, those that separate amplification, and "others." 
     My analysis appears in the "Discussion" document. One of the primary purposes of this study is to show that the rules, and the research that supports them, are somewhat subjective. Obviously, in cases of subjectivity, people will disagree. Thus the "Discussion" document will enable readers to check their own judgments against against mine. I have, in the "Discussion" document, also analyzed every word in every sentence. This should enable parents and teachers who do not feel comfortable with their own skills in analyzing sentences to use some of these sentences as exercises for their children or students. (Some of these sentences will also be used in other areas of this site for review exercises.)

The Syntactic Use of Semicolons

     In exploring the syntactic distinctions made by these forty-five semicolons, I found that 38 (87 %) separated clauses. However, it seems that only 31 (69 %) can been seen as separating main clauses. One of these (# 29) was counted both in the main-clause group and in the "other" group because the entire S/V/C pattern of the clause that comes after the semicolon is ellipsed. Thus some grammarians may not consider it to be a main clause. Eight of the semicolons separate subordinate clauses. This can be seen most clearly in numbers 30-36, where six semicolons separate clauses that are subordinate to the initial "we know."
     The remaining six semicolons (seven if we count # 29) do not separate either main or subordinate clauses. Number three separates a gerundive from the noun it modifies. Numbers eight and nine, both in the same sentence, set off appositives. Number 29, discussed above, separates a full main clause from an ellipsed version. Numbers 39, 40, and 41, all in the same sentence, separate finite verb phrases within a subordinate clause, within an 84-word main clause. (Since none of the finite verb phrases includes a comma, this cannot be considered as falling under the rule that semicolons separate items in a series.)
     Keeping in mind that we are dealing with a short sample from only one writer, we can still draw some important conclusions here regarding the use of semicolons. The general rule that semicolons separate main clauses is valid, but we need to remember that main clauses can become subordinated within other clauses, as in the "we know" example given above. In "Corn-pone," however, Twain used six semicolons (13 %) that cannot justifiably be explained as joining main clauses. If Twain could do it, why can't our students? One could, perhaps, come up with additional rules to justify Twain's use of these semicolons, but that approach would be silly. As it is, most students do not understand, and cannot apply the simple rule that most teachers try to teach. A better approach (a KISS-like approach) would be to enable students to identify clauses, give them the usual, general rules, and then invite students to explore texts on their own to see how writers do or do not follow the rules. Finally, Twain's essay suggests that, in correcting students' writing, we need to think twice before marking as an error any semicolon that does not join main clauses.

The Semantic Use of Semicolons

     It may be a personal bias, but I have long suggested to students that the ability to recognize (and communicate) similarities and differences is the initial building block of human thought. It may have begun with our ancient ancestors when they learned that some things were the same (edible) also but different from non-edibles. Such thinking is central to any type of categorization -- types of trees, types of sweeteners, types of government. And beyond categorization, any comparison / contrast depends, obviously, on the ability to see and communicate similarities and differences. Thus I love to tell students that semicolons separate main clauses, especially if the clauses present contrasting ideas. The semicolons in Twain's essay validate my instruction, but only in part.
     The semantic question is more complex than the syntactic. In both instances, there are questions regarding what any specific writer was formally taught or unconsciously absorbed. Was Twain "taught" to use semicolons to separate main clauses with contrasting ideas? Could Twain identify clauses? Or did he absorb the rules from  what he read? These questions apply to both the semantic and the syntactic issues. But the semantic goes beyond these. What, exactly, are "contrasting" ideas? And, even if a writer does, consciously or unconsciously, use semicolons to separate contrasting elements, do we, as readers, always catch the implicit difference? "He went swimming; she did the dishes" implies, to many thoughtful readers, that he was having fun whereas she was stuck in the kitchen, but not all readers will catch the distinction. Thus, as we look at how a writer uses semicolons to clarify meaning, we need to be especially cautious.
     In analyzing how Twain uses semicolons to separate contrasting clauses, I think I found 21 cases in which I can point to the contrast. In some cases these are simple distinctions between the past and the present, as in numbers 25 and 26. Some of the contrasts are between affirmative statements and negations (# 21, 22, 24, and 29). And he uses the contrast between "the Smiths" and "the Joneses" (# 28), but he does so to argue that the Joneses follow (become similar to) the Smiths. Similarly, he uses seven semicolons to distinguish religious and other groups (30-36), but his purpose in clearly distinguishing the groups is to suggest that most members of all these widely different groups are what they are for the same thoughtless reason. The fundamental same/different perspective is relevant here, but I hesitate to say that his purpose is in the contrast. I counted two of the semicolons (16 & 17) twice, as both contrast and amplification. Interested readers can check the discussion document to see if they agree not only about these two, but also about some of the more complex cases.
     One of the things that surprised me is the number of cases (20) in which I see the second clause as amplifying the first. (Perhaps there are distinctions that I missed?) Textbooks usually suggest that colons or dashes should be used when the second clause amplifies in some way the meaning of the first. Perhaps Twain was a poor student. Or perhaps the textbooks are wrong. Note, however, that cases of amplification still involve the basic same/different perspective, the difference being that what comes after the semicolon further defines the similarity. In some cases (such as 37 & 38), the second clause does not so much amplify as it restates the first in different words. The relationship between such clauses can almost be viewed as one of apposition. Note, in this regard, that two of the semicolons (8 and 9) that I have classified as syntactically "other" literally separate appositives.