Some writers avoid semicolons either because they are not certain of the punctuation mark’s functions or because some people consider it stodgy, or both. It is in fact quite simple and practical to use, but beware of employing one when a comma will do just as well, as in the following examples, each followed by a discussion and a revision.
1. Proponents argue that the surge in foreign demand for US exports will strengthen the value of the dollar; in turn, a strong dollar would increase the demand for imported goods; therefore, the net effect on trade is neutral.
Using two or more semicolons in one sentence to divide independent clauses (in a role sometimes called the weak period) is an error. In such a case, replace one with an actual period and capitalize the next word to begin a new sentence: “Proponents argue that the surge in foreign demand for US exports will strengthen the value of the dollar. In turn, a strong dollar would increase the demand for imported goods; therefore, the net effect on trade is neutral.”
2. It is a strange sort of adventure film, in that it spends as much time in Europe as it does in the rain forest; is as anthropologically curious about the social customs of early-twentieth-century Britons as it is about the indigenous peoples of the Amazon; and cares as much about what is destroyed as what might be found.
When a list of more than two phrases within a sentence consists of one or more phrases that themselves include commas, using commas to divide the longer phrases will confuse readers because the hierarchy of the sentence’s organization is unclear; use semicolons (in the strong-comma function) instead to set the longer phrases apart from each other.
In this case, however, the only comma in the sentence merely sets the introductory phrase off from the rest of the statement, and the organization of the three phrases that follow is clear without resorting to semicolons; use commas instead: “It is a strange sort of adventure film, in that it spends as much time in Europe as it does in the rain forest, is as anthropologically curious about the social customs of early-twentieth-century Britons as it is about the indigenous peoples of the Amazon, and cares as much about what is destroyed as what might be found.
3. The auditor improves information for decision making across the organization by assessing the reliability of performance metrics and monitoring systems the organization has in place; using analytic tools to create lead performance indicators and trending metrics to signal when risk events might be approaching or occurring; and recommending automation of key controls or selected processes to enable effective monitoring.
This sentence does not require semicolons, even with the complication of conjunctions within the separated phrases that function as items in a list—as mentioned above, they are necessary only when one or more phrases within that list themselves include punctuation: “The auditor improves information for decision making across the organization by assessing the reliability of performance metrics and monitoring systems the organization has in place, using analytic tools to create lead performance indicators and trending metrics to signal when risk events might be approaching or occurring, and recommending automation of key controls or selected processes to enable effective monitoring.” (As before, the fact that each phrase begins with a distinct verb strengthens the structure of this sentence.)
In example 2, I can’t see any reason to include the first comma, the one between “film” and “in that.”