# In what tense (present/past) should papers be written?

That is, should it be present tense or past tense?

Should there be a difference between the abstract, main body and the conclusion?

Does the field of publication have any impact?

-
I suggest reading a copy of How to Write and Publish a Scientific Paper by Robert A. Day. You could also get a copy of The Elements of Style by William Strunk Jr. and E.B. White. – user244795 Dec 3 '12 at 17:24
Don't forget about the future tense (for discussion and open problems). :-) – Anonymous Mathematician Dec 3 '12 at 17:55
@user244795 +1 for Strunk and E.B. White. So much valuable information in such a small book. – user4383 Apr 19 '13 at 4:06

The rules of thumb are:

• Established facts are reported in the present tense (“The path of light follows Fermat's principle of least time”). However, you should use the past tense when you refer to previous work in the field (“Maxwell et al. demonstrated clearly in a laser cavity experiment that no mirror is perfect”).
• The experiments, simulations or calculations you performed are narrated in the past tense (“We dissolved the remaining solid in a 5:1 solution of acetone and benzonitrile, and heated to 200°C for three hours.”)
• Discussion of the data presented in the paper uses the present tense (“The results obtained, shown in Fig. 3, clearly emphasize that the cell colonies grew faster on pink toothbrushes than green ones. We attribute this to the color-sensitivity, or kawai factor.”)
• Mathematical proofs are written using the present tense, because going through the proof occurs at the time of reading (“From Eqn. 1, we derive the following system of inequalities”).

Overall, the choice of tenses is actually pretty logical.

-
I'm not sure if I agree with the third example. If the result can be generalised, surely the results show that the cell colonies grow faster, not grew faster, on pink toothbrushes? – gerrit Oct 5 '12 at 19:21
@gerrit I agree: here, as written, it is meant to be a specific statement about the experiment (it is “ the cell colonies grew faster”, not “cell colonies grow faster”). Both are of course possible, but have different meanings… – F'x Oct 5 '12 at 20:23
A trickier case is describing mathematical proofs from older papers. It's "Thurston [4] claimed that 3-manifolds are ..." but "Thurston's argument [4] implies that 3-manifolds are...". – JeffE Oct 5 '12 at 20:42
This is a nice succinct description of tense. In the lab report guidelines I wrote for my students, I took two pages. – Ben Norris Oct 5 '12 at 22:51
@Suresh: The subject of the first sentence is a person, who made his claim at a specific time in the past. The subject of the second sentence is an argument, which implies what it always has and always will, and oh by the way it was first articulated by Thurston. Platonism FTW! – JeffE Oct 6 '12 at 3:15