Day’s rule

‘One special convention of writing scientific papers is very tricky. It has to do with tense, and it is important because proper usage derives from scientific ethics.

‘When a scientific paper has been validly published in a primary journal, it thereby becomes knowledge. Whenever you state previously published findings, ethics require you to treat the work with respect. You do this by using the present tense. It is correct to say, “Streptomycin inhibits the growth of M. tuberculosis (13)”. Whenever you state previously published findings, you should use the present tense; you are referring to established knowledge ...

‘Your own present work must be referred to in the past tense. Your work is not presumed to be established knowledge until after it has been published. If you determined that the optimal growth temperature for Streptomyces everycolor was 37 °C, you should say, “S. everycolor grew best at 37 °C” ...

‘In the typical paper, you will normally go back and forth between the past and present tenses. Most of the Abstract should be in the past tense, because you are referring to your own present results. Likewise, the Materials and Methods and the Results sections should be in the past tense, as you describe what you did and what you found. On the other hand, much of the Introduction and much of the Discussion should be in the present tense, because these sections often emphasize previously established knowledge ...

‘The main exceptions to this rule are in the area of attribution and presentation. It is correct to say “Smith (9) showed that streptomycin inhibits S. nocolor”. It is also correct to say “Table 4 shows that streptomycin inhibited S. everycolor at all pH levels”. Another exception is that the results of calculations and statistical analysis should be in the present tense, even though statements about the objects to which they refer are in the past tense; for example, “These values are significantly greater than those of the females of the same age, indicating that the males grew more rapidly”. Still another exception is a general statement or known truth. Simply put, you could say “Water was added and the towels became damp, which proves again that water is wet”. More commonly, you will need to use this kind of tense variation: “Significant amounts of type IV procollagen were isolated. These results indicate that type IV procollagen is a major constituent of the Schwann cell ECM”’.