Part 1: English Verb Tenses – Forms
This table shows the forms of English tenses for a regular verb (explain) and an irregular verb (find) in the active (explain/find) and passive (was/were explained/found) voices.

	Simple	Perfect	Progressive	Perfect Progressive
Present Active Passive	he explains she finds it is explained It is found	he has explained she has found it has been explained it has been found	he is explaining she is finding it is being explained it is being found	he has been explaining she has been finding it has been being explained it has been being found
Past Active Passive	he explained she found it was explained it was found	he had explained she had found it had been explained it had been found	he was explaining she was finding it was being explained it was being found	he had been explaining she had been explaining it had been being explained it had been being found

(Caplan, 2012, p. 66)

The tenses shown above account for the majority of the tensed verbs used in academic writing (Caplan, 2012). In fact, 98% of the verb tenses used in academic writing are in these three tenses: present simple (70%), past simple (23%), and present perfect (5%) (Biber et al., 1999, in Caplan, 2012, p. 66).

Additionally, verbs can occur in either active or passive voice. About 25% of verbs in academic and scientific writing are in the passive voice (Biber et al., 1999, in Caplan, 2012). The choice of whether to use active or passive depends on various factors. However, in general, when the agent (who or what does the action) is important, active voice is used. When the emphasis is on what was done or what occurred, passive voice is used. Active and passive are also used to increase sentence variety.

Examples

The National Science Foundation (NSF) conducted the study. (active)

The study was conducted last year. (passive)

In the above sentences, passive is used in the second sentence to avoid naming the agent again, which would be repetitive and unnecessary; the agent was already named in the first sentence. As you read articles in your field, note how often and for what purpose active and passive voice is used.

As you probably know, there are two types of verbs in English: regular and irregular. For regular verbs, both the past simple and present perfect are formed by adding "-ed" to the end of the main verb (help/helped, conduct/conducted). For irregular verbs, the past tense form does not add "–ed." Instead, the past simple and past participle are in a different form. The past participle is used for perfect tense forms and passive voice. Sometimes the past simple and past participle form of the verb are the same, but sometimes they are different. Look at some examples below:

Present Simple	Past Simple	Past Participle	Passive
say	said	has/have said	was/were said
make	made	has/have made	was/were made
find	found	has/have found	was/were found
come	came	has/have come	NA This verb does not occur in passive.
describe	described	has/have described	was/were described
include	included	has/have included	was/were included
show	showed	has/have shown	was/were shown
give	gave	has/have given	was/were given
see	say	has/have seen	was/were seen
feel	felt	has/have felt	was/were felt
seem	seemed	has/have seemed	NA This verb does not occur in passive.
meet	met	has/have met	was/were met
tell	told	has/have told	was/were told
learn	learned	has/have learned	was/were learned
choose	chose	has/have chosen	was/were chosen
spend	spent	has/have spent	was/were spent

Remember that the past participle is used for both the present perfect and past perfect (has found, had found), as well as the passive (was found, were found).

Part 2: Verb Tense Use in Scientific Writing

1. Simple present tense is used primarily for the following purposes in academic writing:

Purpose	Examples
to frame the paper The introduction is often in present simple tense. The present simple tense is used to describe what is already known about the topic.	The prevalence of social media means that we often find written language with variation and errors. In this paper, we focus specifically on actual written errors.
to make general statements, conclusions or interpretations about previous research or general knowledge	Social media includes styles of writing that differ from standard usage. Our examination of marine communities associated with oil platforms in Gabon is the first scientific investigation of these structures and highlights the unique ecosystems associated with them. The marine diversity of Gabon is poorly known.
to introduce evidence or support with "there + be"	There are no true coral reefs in Gabon. There are currently 40 offshore oil platforms in Gabon.

2. Simple past tense is used primarily for the following purposes in academic writing:

Purpose	Examples
to introduce a specific study, usually completed by a named researcher	Researchers at Ifakara Health Institute (IHI) were alerted to human rabies deaths and acute distress among families unable to obtain PEP. Subsequent research estimated the burden of rabies in these communities.
to describe the methods and data of a completed experiment	Participants completed a 10-item evaluation scale for each method. We conducted underwater visual fish consensuses using two methods. Benthic taxon and fish species diversity were calculated from the Shannon-Weaver diversity index.
to mark time with specific time markers such as in 2010, after the study, at that time, and previously	After 10 minutes of training, most users were able to log on without problems. Finally, participants were asked if they noticed any errors in the messages they read. On October 12, 2012, we observed pair spawning of red snapper.

3. Simple present perfect tense is used primarily for the following purposes in academic writing:

Purpose	Examples
to introduce a new topic, sometimes using there has/have been	There have been few studies of this issue done. The marine life on these structures has never been studied.
to summarize previous research	Previous research has focused on the deep sea biodiversity of the continental margin. James Pennebaker and colleagues have shown a variety of correlations between personality traits and the use of words.
to describe previous findings or tell the history of an idea	The marine biodiversity of Gabon has not been well studied. Few studies concerning the interpretation of errors have been done to date. A few studies have shown that individual differences in empathy influence some aspects of language interpretation.
to mark time with specific time markers such as since 2009, never, to date, and until now	Since 2010, we have registered over 450 users. Forty thousand oil wells have been drilled in the Gulf of Mexico since the 1940s. The marine life on these structures has never been studied.

Practice: Tenses
For additional verb tense practice, go to this link: Tense Practice Quiz. In the practice exercise, you will complete the sentences using the correct verb tense. Be sure to pay attention to any time markers that occur in the sentence.

Caplan, N. (2012). Grammar choices for graduate and professional writers. Ann Arbor: University of Michigan Press.