The passive and active voices and when to to use them
The subject (doer) is put at the beginning of the sentence and performs and action. The object (done to) of the action is placed after the verb at the end of the sentence. In the following sentence 'The team' is the subject, the 'optimum pH' the object.
The team calculated the optimum pH.
The active voice:
- is usually more concise than the passive voice
- puts the subject at the sentence beginning - better if the subject is at least as important as the object
The object of the action is placed at the beginning of the sentence. The subject is placed after the verb. This sentence construction sometimes needs additional words with the main verb, such as 'is, was, are, being ...[verb]...by'
The optimum pH was calculated by the team.
The passive voice:
- sounds more formal so invites use in science
- can sound duller
- can use more words
- enables a more impersonal tone
When should I use passive, when active?
Some believe that you should not use the active voice in formal scientific writing because scientific writing should be impersonal. Ultimately, you should use the style of language with which supervisors and co authors feel most comfortable. Further, some journals provide guidance on writing style and prefer authors to use the active voice (always read a journal’s ‘Instructions for Authors’).
Using the active voice does not mean you need to use a person’s name or personal pronoun (‘I’ or ‘we’). Take the example: ‘Process X improves yield.’ This is the active voice but does not need a personal pronoun. The passive version is fine ‘Yield is improved by using process X.’, but it uses more words.
I and We
It is now acceptable to use 'we' in formal science writing. Further, in thesis writing the occasional use of 'I' can be appropriate - for example when indicating that you have decided to use a particular method from a number of alternatives. However in disciplines such as the physical sciences, using the first person ('I') is often less acceptable. So check with your supervisor or PI, or other colleagues and a journal's Instructions for Authors.
If you are uncertain about what a passive or active style reads like, compare the following two abstracts. The passive version has nine instances of the passive voice and 131 words. The active version has six instances of the active voice and three in the passive; the word count is 122 words.
Example 1: passive style
Biosecurity is defined as a set of measures to protect animals and crops from the risk of disease. It is considered important in pig production, and several routine measures are employed by farmers (e.g. cleaning, disinfection, segregation). However, air as a potential vector of pathogens has long been disregarded. Filters for incoming and recirculating air were installed into the ventilation system of one of two barns at a fattening piggery. Over three consecutive fattening periods, the lung health of pigs in the filtered compared with the unfiltered barn was evaluated. Air filtration was easily introduced into the existing ventilation system. Better lung health was found in animals from the barn equipped with recirculating air filtration modules. Therefore, air filtration systems in animal rearing enclosures should be recommended by animal healthcare professionals.
Example 2: active style
Biosecurity is defined as a set of measures to protect animals and crops from the risk of disease. It is important in pig production, and farmers routinely employ several measures (e.g. cleaning, disinfection, segregation). However, air as a potential vector of pathogens has long been disregarded. We installed filters for incoming and recirculating air into the ventilation system of one of two barns at a fattening piggery. Over three consecutive fattening periods, we compared the lung health of pigs in the filtered and unfiltered barn. Air filtration was easily introduced into the existing ventilation system. Animals had better lung health in the barn equipped with recirculating air filtration modules. Therefore, animal healthcare professionals should recommend air filtration systems in animal rearing enclosures.
(Adapted from: Wenke C. et al. (2018). Impact of different supply air and recirculating air filtration systems on stable climate, animal health, and performance of fattening pigs in a commercial pig farm. PloS One 13.3: e0194641)
The active voice is appropriate:
- when readers/journals express a preference/expect the active voice
- to avoid/cut down excessive use of words
- to identify the subject and/or take responsibility.
The passive voice is appropriate:
- the most readable text is often a combination of active and passive voice (as in example 2 above)
- to achieve a balance with the active voice, particularly in the ‘methods’ section of a manuscript
- when the subject is not known, obvious or irrelevant:
Artificial intelligence has been the subject of considerable research for decades. (By whom? … It doesn’t matter.)
- when the object/recipient is the main topic:
These dangerous emissions are produced by diesel engines. (When the focus is ‘dangerous emissions’ and not diesel engines.)