More Principles of Scientific Writing

In the last post, we covered the first principle of scientific writing dealing with subject-verb separation.  We are using an example of scientific writing (an abstract) selected randomly from the literature to examine principles of writing proposed by Gopen and Swan (1990).  In this post, we'll consider the "stress position" and the "topic position" and how to use these concepts to improve our writing.

The Stress Position

Readers expect to see the point of a sentence appear in what is known as the "stress position", i.e., the place of emphasis in the sentence.  The idea here is that readers naturally look for the “pay-off” at the end of a sentence.  We begin reading a sentence with a sense of expectation that builds as we approach the reward at the end of the sentence.  Our original example does not do this:

The discrete-dipole approximation (DDA) for scattering calculations, including the relationship between the DDA and other methods, is reviewed. Computational considerations, i.e., the use of complex-conjugate gradient algorithms and fast-Fourier-transform methods, are discussed. 

Instead, the first two sentences in the original example end limply with “is reviewed” and “are discussed”.  These sentences leave the reader feeling annoyed by promising, but not delivering information. On top of this, the sentences are more difficult to follow (because of undue separation of subject and verb) and are not very interesting (being written in passive voice).

To revise, I moved the verbs closer to their subjects and tried to place the material to be emphasized at the end of the sentence:

We review the discrete-dipole approximation (DDA) used in scattering calculations and its relationship to other methods.  Other computational considerations include the complex-conjugate gradient algorithms and fast-Fourier-transform methods.


The stress position is where the reader needs and expects closure and the information that is being emphasized ("...complex-conjugate gradient algorithms and fast-Fourier-transform methods."). 
We can summarize the first aspect of the stress position as:  "Save the best for last."  However, we also have to worry about the beginning of the sentence:  the topic position.

The Topic Position

The topic position provides the reader with perspective.  Whatever begins a sentence is what the reader interprets as being what the story is about: "Squirrels hide acorns" vs. "Acorns are hidden by squirrels".  Both sentences are correct, but the first indicates to the reader that the discourse is focused on squirrels, whereas the second emphasizes acorns.  If you use the first version, but your topic is actually oak trees (or seed dispersal), then you will confuse your readers.

This concept of topic position gets tricky when we use first person in technical writing.  With sentences such as: "We review several methods for computing light scattering." or "We studied the role of salinity in determining distribution of coastal plant species.", the emphasis is placed on us, the investigators, rather than on the topic under investigation.  So let's reconsider my revision above.  The second sentence seems fine with respect to subject-verb separation, the stress position, and the topic position:

Other computational considerations include the complex-conjugate gradient algorithms and fast-Fourier-transform methods. 

The topic ("computational considerations") is introduced to the reader at the beginning of the sentence.  The information that is to be emphasized ("complex-conjugate gradient algorithms and fast-Fourier-transform methods") is placed at the end of the sentence, where the reader expects it.  And the subject and verb are in close proximity ("considerations include").

The first sentence, however, has the problem of emphasizing the authors ("We review...") instead of the science topic.  This first-person style is certainly acceptable and not a major problem, in my opinion, if it is used sparingly.  But if we wanted to revise this sentence to adhere to the third principle, how would we do it?  Here is one possibility (I'm making some assumptions here, being unfamiliar with the topic, but it illustrates the point):


The discrete-dipole approximation (DDA) is [often] used in scattering calculations, but its accuracy is unclear in relation to that of other methods.

This sentence now tells the reader what the topic is (DDA), places the point of the sentence (its questionable accuracy) in the stress position toward the end of the sentence, and also explains the "problem" that the paper will address. All the subjects are in close proximity to their verbs.  Although the sentence is now written in passive voice, this is the choice one must make to ensure the reader knows what the actual topic is (acorns vs. squirrels).

The first-person version "We review..." is perfectly fine, as is "This study provides...".  However, the new version puts the actual topic (DDA) in the topic position and also tells us more explicitly why the study needed to be done.  Another option would be to combine the first two sentences:

The discrete-dipole approximation (DDA) is [often] used in scattering calculations, but its accuracy is unclear in relation to that of other computational methods such as complex-conjugate gradient algorithms and fast-Fourier-transform methods.   

This sentence is quite long, but flows well and is easy to understand.  It also prepares the reader for the next sentences that explain what was done and what the results were:


The accuracy of the DDA was tested in computations of scattering and absorption by different targets: isolated, homogeneous spheres and two contiguous spheres. For dielectric materials ((¦m¦ ≲ 2), the DDA permitted calculations that were accurate to within a few percent.

We now have covered the first three principles proposed by Gopen and Swan:


1.    Follow a grammatical subject as soon as possible with its verb.

2.    Place in the stress position the "new information" you want the reader to emphasize. 

3.    Place the person or thing whose "story" a sentence is telling at the beginning of the sentence,  in the topic position.