One of the questions scientists ask often when they write a manuscript is “Which tense do I use in the Introdution, Results, or Discussion when I describe the methodology, discuss my findings and talk about other scientic literature?”
Here is a wonderful pdf with a summary of which verb tense to use when, written by Dr. Ben Mudrak, that I myself refer to frequently.
If you want a quick recap, here it is:
the simple present tense (e.g. “Gene X is required for intestinal cell differentiation”)
the simple present tense
for widely accepted facts (e.g. “DNA is composed of four nucleotides.”)
when a specific result/figure/study is the subject of a sentence (e.g. “the results of their study indicate that…”)
the present perfect tense
for results from previous studies that are still relevant (e.g. “Smith et al. have shown that…”)
the past tense
for methods used in previous papers (e.g. “they samples 96 swamps”)
for statements that are no longer true (e.g. “bacteria were believed to lack introns”)
Of course, other tenses can be used to, such as the past perfect tense (e.g. “patients who had elected to undergo surgery completed questionnaires”) or the past progressive (e.g. “while patients were preparing”).
the past tense to describe what was done during the course of the study (e.g. “proteins were extracted”)
the past tense to describe the experiments completed before the writing up of the study (e.g. “we detected…”)
the present tense to describe specific data, results, figures, tables, sections, or the entire study (e.g. “our results indicate that…”, “in this study, we report…”, “our study demonstrates…that magnesium is required…”, “Figure 1 shows…”, “Table 2 explains…”)
The tenses used in the Discussion follow the same rules described above. Additionally, the future tense is used for directions for additonal research (e.g. “further research will elucidate…”).
The tenses used in the Abstract correspond to the matching sections described above.
I hope this was helpful. Enjoy your writing and good luck!