Lesson: Connecting Sentences

Scientific writing in English requires you to use a variety of sentence types and lengths. Sometimes you want to write a very short and simple sentence to bring extra clarity or emphasis to an idea. Other times you want to include several ideas in a sentence to show multiple connections or relationships between ideas. In other words, you need to use all kinds of sentences—short and long, simple and complex—to write about your scientific research. This requires you to be able to write sentences with more than one clause. Correct punctuation varies depending on the type of word or phrase used.

Clauses
A clause is a group of words connected by a verb. There are two types of clauses: independent and dependent. An independent clause is a complete sentence because it has a subject with a finite verb that can carry verb tense. A dependent clause is not a complete sentence and often begins with a subordinating conjunction such as “because” or “if."

 

Part 1: Using Subordinating Conjunctions to Combine Clauses
Subordinating conjunctions include the following words and phrases commonly found in scientific writing: because, if, although, while, unless, after, before, as, whereas, since, despite the fact, when, whether, in order that, once, so that, even though.

The subordinating conjunction begins the dependent clause and indicates its relation to the rest of the sentence. An example is “although the advantages were evident," which is not a complete sentence. It needs to be combined with an independent clause to create a grammatically complete sentence.

Sometimes the dependent clause comes before the independent clause:

Although the advantages were evident, the director decided not to follow the plan.

Other times the dependent clause comes after the independent clause:

The director decided not to follow the plan although the advantages were evident.

Punctuation Guidelines: Place a comma immediately after the dependent clause when it comes before the independent clause (see sentences above). Commas are not commonly used between the two clauses when the independent clause comes first—unless a strong contrast is expressed with "whereas" or "while” as in the examples below: 

Spiny lobsters were found in groups of 2–4 individuals and were of small size (10–15 cm total body length), while slipper lobsters were often found alone or in pairs and attained larger adult sizes (20–25 cm total length).*

The former were dominated by a solitary cup coral, Tubastraea sp., whereas the latter were dominated by the barnacle Megabalanus tintinnabulum.*

 

Part 2: Using Coordinating Conjunctions to Combine Clauses
Two independent clauses are often connected with a coordinating conjunction such as and, but, so, or, yet, nor, for. To help us remember which words fall into this category, we sometimes refer to them by using the acronym “fanboys” (for, and, nor, but, or, yet, so). The following examples use coordinating conjunctions:

There are no true coral reefs in Gabon, and most of the largely unmapped reefs are rocky.*

Extensive oil exploration and development began onshore in Gabon in the 1950s, but offshore exploration did not begin until the 1960s.*

Large snappers (primarily L. dentatus) were often deeper and not easily observed, so the actual standing stock of fish biomass on these platforms is likely much higher than our estimates suggest.*

Punctuation Guidelines: When connecting two independent clauses with a coordinating conjunction, place a comma before the conjunction.

 

Part 3: Using Sentence Connectors to Combine Clauses
Another way to connect independent clauses is with sentence connectors, which are sometimes called transitional adverbs. These include the following words and phrases: therefore, however, in addition, nevertheless, in contrast, for example, in other words, moreover, consequently, for instance, as a result, thus. These draw more attention to themselves than do the subordinating conjunctions and coordinating conjunctions introduced above. Their size and punctuation tend to “stop” the readers and make them think about the relationship. Therefore, you want to use them sparingly.

Punctuation Guidelines: Place a semi-colon between the two clauses. If the sentence connector comes at the beginning of the second clause, a comma usually follows it. If the sentence connector is not the first word in the clause, it will be preceded and followed by a comma. Note: the semi-colon can be replaced with a period. The following are examples: 

Most of the fish biomass on the platforms was composed of pelagic species with broad biogeographic distributions. However, much of the observed species richness consisted of demersal species, many of which had distinct and unique assemblages.*

The authors used the punctuation above, but they also had the options below:

Most of the fish biomass on the platforms was composed of pelagic species with broad biogeographic distributions; however, much of the observed species richness consisted of demersal species, many of which had distinct and unique assemblages.

Most of the fish biomass on the platforms was composed of pelagic species with broad biogeographic distributions. Much of the observed species richness, however, consisted of demersal species, many of which had distinct and unique assemblages.

Useful Subordinating Conjunctions, Coordinating Conjunctions, and Sentence Connectors (adapted from Oshima & Hogue, 2006)

Meaning/Function

Subordinating Conjunctions

Coordinating Conjunctions

Sentence Connectors 

to introduce an additional idea

 

 and

 in addition
 furthermore
 moreover

to introduce an opposite idea or contrast

 although 
 though
 even though 
 whereas
 while

 but
 yet

 in contrast
 however
 nevertheless
 instead

to show similarity

 

 

 likewise
 similarly

to introduce an example

 

 

 for example
 for instance

to introduce a result

 

 so

 as a result
 therefore
 consequently
 thus

to introduce a cause

 

 for

 

to introduce a choice or alternative

 if
 unless

 or

 otherwise
 alternatively

to introduce a restatement or explanation

 

 

 in fact
 indeed
 that is

to introduce order (time)

 before
 after
 until
 when
 while
 as soon as
 since

 

 first
 second
 next
 after that
 meanwhile
 subsequently
 finally

to introduce a summary or conclusion

 

 

 clearly
 in brief
 in conclusion
 indeed
 in short
 in summary

  

Part 4: Using Relative Clauses
Another way to combine ideas (and clauses) in your sentences is through relative clauses. These are the parts of sentences that begin with a relative pronoun such as “who” or “which” (although in some cases it is possible to delete these words, leaving only a reduced version of the clause). Relative clauses are an excellent way to combine ideas or add information to a sentence in your scientific writing. There are two types of relative clauses—non-restrictive and restrictive—which vary in meaning and punctuation.

Non-Restrictive Relative Clauses
A non-restrictive relative clause adds extra information to a noun in the main clause for the purpose of clarifying, describing, or explaining it. Use the relative pronoun “who” (or “whom” when in object position) to refer to humans; use “which” for non-humans; and use “whose” for all possessive forms. The following are examples of sentences with non-restrictive relative clauses:

These platforms are in sharp contrast to much of Gabon's marine environment, which is dominated by soft sediment communities.*

Longitude and depth, which were significantly correlated with latitude and platform area respectively (p<0.05), also were excluded from the analysis.*

Several amphi-atlantic species, which occur only around oceanic islands, were observed on the oil platforms off Gabon.*

Alternatively, a non-restrictive relative clause can serve to extend the meaning of the main clause (especially when placed at the end of the sentence) by adding a result or implication.

The addition of artificial reefs in the deep sea is likely to increase ecological connectivity, which will have important biogeographical consequences.*

Punctuation Guidelines: Place a comma before the restrictive relative clause. If the restrictive relative clause comes in the middle of the sentence, also place a comma after the relative clause.

Restrictive Relative Clauses
The restrictive relative clause actually identifies the subject rather than simply provide extra information about it. Use the relative pronouns “who” or “that” (or “whom” when in object position) to refer to humans; use “which” or “that” for non-humans; and use “whose” for all possessive forms. The following is an example of a sentence with a restrictive relative clause:

Rigs-to-reef programs which allow decommissioned oil platforms to stay in place have gained some support by governmental and non-governmental organizations.*

Note: The authors could have replaced “which” with “that” in this sentence.

Punctuation Guidelines: No commas are used.

Differences in Meaning
Non-restrictive and restrictive relative clauses appear almost identical (except for the use of commas), but the meaning can be quite different.

Non-restrictive relative clause: Survey questions, which focused on attitudes toward exercise, were open ended. (Meaning: All of the survey questions on this survey were focused on attitudes toward exercise.)
Restrictive relative clause: Survey questions which focused on attitudes toward exercise were open ended. Survey questions which focused on medical history were multiple choice. (Meaning: There are different kinds of survey questions. Those focusing on attitudes toward exercise were all open ended format. Multiple choice format was used for another topic.)

Non-restrictive relative clause: The surveys, which were conducted via email, consisted of 20 questions. (Meaning: All of the surveys consisted of 20 questions.)
Restrictive relative clause: The surveys which were conducted via email consisted of 20 questions. The surveys which were conducted in the office consisted of 25 questions. (Meaning: There were two different surveys, and they are identified by the place in which they were conducted.)

Using Reduced Forms of Relative Clauses
It is possible to reduce relative clauses to make your writing more concise. However, do not do this if it will create ambiguity or other possible confusions for the reader.

Reducing a non-restrictive relative clause
When the clause comes at the end of a sentence, the relative pronoun (which or who) can be deleted and the verb changed to an "-ing" form.

Original Form: Two similar medications were distributed, which caused confusion among the patients.

Reduced Form: Two similar medications were distributed, causing confusion among the patients.

If the verb is a form of “be”, delete both the relative pronoun (which or who) and the verb.

Original: The first treatment, which was a series of five exercises, was introduced during the first week.

Reduced Form: The first treatment, a series of five exercises, was introduced during the first week.

Reducing a restrictive relative clause
Delete the relative pronoun (which, who, that) and change the verb to an "-ing" form.

Original Form: Survey questions which focused on attitudes toward exercise were open ended. 
Reduced Form: Survey questions focusing on attitudes toward exercise were open ended.

If there is a “be” verb, delete both the relative pronoun (which, who, that) and the “be” verb.

Original Form: Surveys that were completed before the final treatment were discarded.
Reduced Form: Surveys completed before the final treatment were discarded.

 


Oshima, A., & Hogue, A. (2006). Writing academic English (4th ed.). White Plains, NY: Pearson Longman.

* These examples come from the following reading: 
Friedlander, A. M., Ballesteros, E., Fay, M. & Sala, E. (2014). Marine communities on oil platforms in Gabon, West Africa: High biodiversity oases in a low biodiversity environment. PLoS One 9(8), 1-15. http://dx.doi.org/10.1371/journal.pone.0103709