Tense and verb form for each kind of claim
In English scientific writing the tense and form of a verb tell the reader whether a statement is new or established knowledge and how certain the writer is of it, so each kind of statement in a document takes its own tense.
Why tense matters
Using the correct tense is one of the most important aspects of clear scientific writing in English, because a clear distinction between new and old knowledge is mandatory; in some other languages, such as German, tense appears to be less critical to meaning. Verb tense is an important component of writing with clarity and focus. The tense in which a text is written can make a subtle difference to its meaning.
The tenses of scientific writing
The main tenses used in science reporting are the present and the past, with the perfect and future tenses used rather sparingly. Books on linguistics recognise only two tenses, present and past, and treat the others as aspects formed with the auxiliaries will (future), have (present perfect), had (past perfect) and be (progressive), though for simplicity the more common word tense is used for them too. Each section of a journal article contains anticipated conceptual components, each of which can take a specific tense that conveys its perspective of time and degree of certainty. Most of the conceptual components in a journal article are expressed in the past tense; the exceptions that take the present are the pertinent background to a known research problem and the actual hypothesis in the Introduction, and recommended future research and the research consequence in the Discussion.
Established knowledge
In scientific documents the present tense reports established knowledge: known facts, general knowledge, established findings and previous results. Known facts and general knowledge are usually easy to identify because they concern familiar information, but established findings may be more difficult to recognise. The textbook definition of an established finding is any result that has been published in a credible primary source. A primary source gives the full description of the original research, as a journal article reporting original research findings could, and a secondary source comments on, analyses, interprets or contradicts those findings, a review paper being a good example. What makes a source credible is somewhat more arbitrary; within the sciences a credible source could be a peer-reviewed journal or another recognised scholarly source, such as an article issued by a university publisher.
Methods and materials
Methods applied and materials used in the current study are reported in the past tense, because the section describing them gives an account of how the work was conducted. Although some authors would argue that their method is a general recipe that should appear in the present tense, the method description for the current study must be in the past even if the method is an established procedure. Past tense for completed methodological action is the least controversial of all the uses of tense in a journal article, probably because it usually pertains to a physical rather than a cognitive effort: the reactive protocols were decomposed into mechanistic steps, not are decomposed. The source of materials is expressed in the past as well, as in data that were, not are, from a named 1992 survey. The present perfect is surprisingly common in research writing, and its meaning is up to the present time, as in the research problem the causes have been unresolved. For the current authors' completed experimentation, which lies in the past, it is grammatically distracting, so syndecan-1 expression has been measured becomes was measured.
Results
Results are described strictly in the past tense. Using the past tense for new findings, including the writer's own, is perhaps the most important aspect of proper science writing; the past tells the reader that the findings are new and previously unpublished. Many authors are highly enthusiastic about their findings and are tempted to report them in the present, as in the new method is superior to the old one, which is clearly incorrect because the finding is neither published nor a generally known fact. Result statements, such as comparisons, observations and trends, are cognitive efforts that express pastness and thereby connote understatement: there were significantly more ridge deficiencies in the coronal halves, something was, rather than the truism that something is.
Tables and figures
Tables, figures, appendices and other displays contained in the manuscript are referred to in the present tense, because they are part of the actual report or manuscript, as in Table 2 lists the individual percentages. The active voice helps in such sentences, since the passive may encourage the erroneous use of the past tense, which gives a second good reason for the active voice there. Work with tenses that is not quite right can affect a document's tone, and in one writer's experience figure legends are a crucial consideration here, often needing far more work in this respect than authors are prepared to give them.
Hypotheses, objectives and conclusions
The statement of a hypothesis consists of verbs of a mixed tense. Stating the hypothesis is a past cognitive effort, so it takes the past just as a physical action in the Methods does, while the actual hypothesis is meant to be a timeless truth in the present: we hypothesised that the enhancement of the free radical level in the tissue increases the AB neurotoxicity. The act of stating an objective in an Introduction arguably belongs in the past as well, like the act of stating a hypothesis; the statement was made before the experimentation, which justifies the past perfect (had been hypothesised), but the past perfect seems stilted beside the simple past (was hypothesised). The conclusion in a Discussion is another case of the past instead of the present, as in the enhanced free radical level in the tissue increased the AB neurotoxicity. An understated, modest conclusion is viewed as an author's respect for the scientific method and for peers, and a more certain conclusion may be relinquished to other authors, who may convey the information in the Introductions of their own papers as accepted by the discipline, in the present tense.
Other researchers' findings
Attribution, referring to other researchers or attributing previous findings to other authors, is given in the past tense, as in Jones et al. reported similar findings. Some authors prefer the present perfect for attributions, as in Jones et al. have reported similar findings, which is not wrong by any standard, but if a document limits its tenses to the simple present and the simple past, it makes sense to use the past in attributions too. Other guidance instead uses the present to describe a published work, as in Smith and Jones report a 33% survival rate in the test population.
Welles has reported that is better as Welles reported that, since the past tense is more appropriate for the past action of reporting, and even better may be to avoid the non-thematic focus on the investigator in the subject position: administration of the synthetic glucocorticoid dexamethasone beginning at the defined commitment stage inhibited differentiation and mineral deposition in MC3T3-E1 cells. The present perfect, as in Smith has shown, is frequently used for conveying the results of other investigators, and it is inexplicitly intermediate between unaccepted certainty, expressed in the past tense, and certainty, expressed in the present. Perhaps the present perfect, expressing up to and including the present, renders more presentness and thus credibility to the statement, and this use seems justifiable for shows, in contrast to reported, which is clearly limited to a past time.
The present alone, as in protein A is larger than protein B (Smith, 1990) or there are significantly more ridge deficiencies … (Smith, date), is thematically focused and conveys that the current author, the discipline or both accept the statement as valid, a timeless truth; where that acceptance is the intent, the present is explicit compared with the present perfect, as in sialyl Lewis antigens expressed on carcinomas bind, not have been shown to bind, selectin ligands on endothelial cells. Past plus present, as in Smith (1990) confirmed that protein A is larger than protein B, has the same meaning with the emphasis on the previous investigator, and the current author and discipline accept the statement. In Smith reported that protein A is larger than protein B, it was reported by Smith that… and according to Smith…, the statement is solely the previous investigator's responsibility. Past plus past, as in Smith reported that protein A was larger than protein B, is essentially the same, but the inference is that the current investigator is less accepting of the statement. Present perfect plus present, as in Smith has reported (Smith, 1960) that protein A is larger than protein B, carries the inference that the current author, the discipline or both accept the statement, and using it to convey recently is grammatically incorrect because the citation fixes the time in the past.
Misagreement in time
Most misagreements in time are a dissonance, but those in which the present tense conveys certainty are nonprofessional in tone. The more common revision is into the past tense, except for the few conceptual components for which the present, or the present perfect, is appropriate.
Participles and progressive verbs
Two verb forms contain an -ing unit: the present participle of a participial phrase, which is frequently used, and the progressive verb of a progressive phrase. The present participle functions primarily as an adjective, but as a verbal it keeps verb-like qualities such as tense. The present progressive is used infrequently, if at all, in research writing, possibly because of its informal narrative pattern, built on sentence constituents focused on an agent and an action.
A participle in a preliminary interpretation
A preliminary interpretation states information one conceptual level above a result statement. In a Results sentence reporting that band shifts and new bands were consistent with the predicted bands, indicating that the plasmid integrated into the chromosome, the present participle indicating denotes a timeless truth rather than a circumspect preliminary interpretation. The past tense of the revision a consistence which indicated is circumspect, befitting the care with which the research was performed and interpreted. The past form needs a which that inexplicitly modifies more than one of the constituents or even the whole sentence, and this which, often termed the vague which, ostensibly justifies the antecedent marker consistence, which identifies the inexplicit antecedent. The marker consistence may seem a hypercorrection and redundant, so despite its vagueness the adjective clause with the inexplicit which alone, which indicated, may be the preferred option. The frequent use of a present participle for a preliminary interpretation in the Results connotes a timeless truth, a certainty characteristic of a non-professional tone, and turning the present participle into a past participle minimises that certainty.
A participle beside past constituents
In the Introduction sentence unlike the previous study focusing on plasma alone, in the present study the function of the erythrocyte as well as plasma was tested, the present time of the participle focusing is inconsistent with the past focus of the other constituents, previous study and was tested. Turning it into the past participle focused avoids the misagreement, and both participles modify the noun study as adjectives. Study focusing on also personifies an inanimate subject, which study focused on does less.
The progressive verb
The progressive verb is too narratively current. In although many researchers are looking for cementum-specific markers (that differentiate cementum from bone), their existence is still uncertain, the narrative comes from the ongoing present action of are, the agent researchers and the informal narrative verb looking. Replacing the adverbial clause with a tenseless prepositional phrase de-narrativises it: despite wide-spread interest, existence is still uncertain of cementum-specific markers that differentiate cementum from bone. In a Discussion, the present study may also be contributing to understanding magma transport mechanisms at mid-ocean ridges uses contributing, an ongoing present action, in misagreement with a consequence of past research, and the present tense may also contribute conveys a time-independent consequence in the present and even the future. The highly informal narrative progressive is, like a present participle used for a preliminary interpretation, characteristic of a non-professional tone, and tenseless syntactic alternatives or the present tense can replace its narrativism.