A common issue for many authors when constructing their scientific manuscript is deciding when to use present or past tense. This is often easier in some sections than others, such as in the results section when the use of past tense is more natural (e.g., We observed a change in ABC expression...). However, many authors get tripped up when trying to determine if they should use present or past tense in their Abstract. The answer is you should use...both (typically)!
So here are a few things to keep in mind when deciding what tense to use in your Abstract (or other sections as well):
1) Your Results - use when talking about your actual results or observations
Whales swam 4 km further in cold water than in warm water.
Whales swim 4 km further in cold water than in warm water.
2) Past Research
For example: Previous studies have observed that stem cells are sensitive to extracellular calcium levels.
NOTE: This is not usually seen in Abstracts as many journals frown upon using references in this section.
1) General Facts
Gene expression depends on the concentration of transcription factors within the nucleus.
2) Talking about your study - when your study is the subject of the sentence you should use present tense
In this study, we indicate that colon cancer can be cured by beer consumption.
3) Conclusions or Interpretations:
These results indicate that EGCG can promote the proliferation of neural stem cells.
If you now consider how Abstracts are structured, you can properly assign the tense that should be used in each 'section' of the Abstract. The structure is typically as follows:
Background/Objective: Here, you are generally talking about established facts or stating the purpose of the study, therefore use present tense.
Methods: This is what was done in your study, therefore use past tense.
Results: This is what was found in your study, therefore use past tense.
Conclusion: This is the interpretation or overall findings of your study, therefore use present tense.
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