Especially for those in technical fields, who typically write scientific reports and coordinate their own research findings with those of other researchers, decisions about the proper verb tense to use in a given situation can be befuddling. A quote by Groucho Marx is instructive here, as Groucho once quipped: “I have had a perfectly wonderful evening, but this wasn’t it.” Because Groucho employs the perfect tense here (using “have had,” which suggests both present and past), he correctly notes that the wonderful evening could have been on any other night in his life.

The first rule of thumb is to word your sentences in such a way that verb tenses are simple and consistent. The easiest way to simplify context for both yourself and your reader is to use present tense when possible, because it is automatically reader-friendly and readily understood. But there is obviously more to this issue. Read on:

An accepted practice is that scientific truths, facts, and things happening during the reading of a paper can be treated best in present tense.

Nickel is generally deposited from sulfate, sulfate-chloride, or sulfamate electrolytes with or without additives.

This paper evaluates material deformation in the brittle and ductile regimes.

Your own findings or experimental procedures, the actual experimental procedures and results of others, and physically past events should usually be treated as simple past tense.

A drop of HNO3 was added to bring the distilled water to pH 3.

In the 1930s, it was fashionable for scientists to write memos only in the passive voice.

Future tense (using “will” or “shall” with a verb) is usually reserved for those things not yet completed. This tense is most useful when you want to talk about future events.

Copper use will become more sophisticated as new exploration technologies and new extraction techniques develop.

Finally, the perfect tense (using “has,” “have,” or “had” as a helping verb) comes in handy when you are writing about a “double time”—that is, when you need to stress that one thing happened before another, or that something began in the past and was continued thereafter.

This particular radiometer has been used since 1985.

Scientists had argued about the existence of molecules for centuries before it was universally agreed that matter was discrete rather than continuous.

Contrary to what some writers think, you certainly may switch verb tense within a paragraph (even within a sentence, for that matter); you simply must be certain that the context implied by the verb tense matches the intended meaning.