Active versus Passive Voice
We are discussing some principles of scientific writing as proposed by Gopen and Swan (1990). But let's make a brief detour at this point to consider active versus passive voice. In our previous examples, we did some shifting from passive to active voice and vice-versa. Some people misunderstand what is meant by active voice, thinking that it only involves first-person subjects: "we discuss this...I review that..." or involves a form of the verb to be: "I am a scientist."
In actuality, a sentence written in passive voice has the subject acted upon by the verb. For example:
"Accurate calculations are permitted by DDA." "The method is reviewed." "John is loved by Mary."
In active voice, the subject is doing the action. The same sentences written in active voice:
"DDA permits accurate calculations." "We review the method." "Mary loves John."
Use of the passive voice is prevalent in scientific writing and is a big part of why technical writing can sound stilted (or even "tortured" as CPP puts it): "Data analysis was preceded by log transformation." There are many other examples, perfected by politicians, in which this is carried to the extreme: "Mistakes were made." As illustrated above, the active voice makes sentences come alive--and also tends to require fewer words.
However, there are instances in which the passive voice is the proper choice.
--When it makes sense to emphasize the receiver of the action. The example I gave in the previous post was "Squirrels hide acorns." (active) versus "Acorns are hidden by squirrels." (passive). If your topic is oak trees (and acorns), you want to select the passive voice version because this tells the reader that you are going to be talking mainly about acorns, not squirrels.
--For variety or when the flow of the paragraph would be improved: "One aspect of the nitrogen cycle can be understood through an examination of microbial processes. These processes . . ."
--In the Methods or Experimental section of a paper where repeated use of first person or people's names would be awkward: "Initially, the experimental plots were clipped to remove standing vegetation and then amended with a slow-release NPK fertilizer."
--In an abstract: "Feeding trials were conducted to assess the role of phenolic compounds in plant palatability."
So to summarize active vs. passive voice, you can use active voice to liven up your writing and be less wordy at the same time. These considerations must be balanced, however, against what subject you wish to emphasize and if passive construction is more appropriate. The key is to make your selection coincide with the reader's needs and expectations.