Correction: 过去式、现在式应为过去时、现在时。

科技英语时态有一些规矩（rules, 没有灵活性可言），我们写文章时必须遵守。下面，我们用加重的黑色字体来标明这些规矩。但是，有些地方，两种时态（比如过去式、现在式），都可以用。不信？请往下看。

为了便于理解、应用，我们按科技论文的写作框架来讨论英语时态的用法。

1. Introduction （引言）

In the introduction, we need to cite publications. （在引言部分，我们会引用一些发表的文章。）

These are common practice.

1) Use the past tense when a sentence starts with a publication. (用主动语态叙述已经发表的文章时，用过去式；不建议用现在完成式。)

For example: Ren et al. (2015) noted a dramatic increase in publication by Chinese authors in SCI journals during the 2000s, thanks in part to the cash reward and promotion criteria set by the (Chinese) system.

Note that even though the publication is recent, I still use the past tense, “noted.” （大家注意到上面引用的“文章”还很新，是去年的。我依然用了过去式。）

Note also that I have no authority to make you follow this rule; but from now on you should pay attention to how your colleagues write when you read their papers.（不过，我不是“语法法官”，你不必太把我当回事。最好的办法是看看你的同行是如何写文章的。）

2) Use the present tense for a result/fact that remains true today, even though the result/fact was obtained 100 years ago.（在叙述一个事实时，用现在式。）

For example:  The Gulf Stream is（用现在式，因为是事实）the most powerful western boundary current on Earth, which was discovered and confirmed（用过去式，因为已经发生了）by sailors and scientists hundred years ago.

3) Use mixed (say past and present) tenses in one sentence.（一个句子中的时态不必统一。）

If you don’t like the sentence I made up in 2), here is one from Wikipedia: European discovery of the Gulf Stream dates （因为是事实）to the 1513 expedition of Juan Ponce deLeón, after which it became（已经发生了）widely used by Spanish ships sailing from the Caribbean to Spain.

4）The last paragraph of the introduction maps out the paper. Use present tense.

It often goes like this: “The rest of this paper is organized as follows. In Section II, the procedure of the xxx method is presented.  In Section III, the proposed method is tested using 66 images with different kinds of textures. Finally, Section V presents the summary of the paper.”

Note that the last sentence is perfectly understandable for native and non-native speakers. In fact, most native speakers may not pay attention to the grammar (as they were never really taught the way we non-native speakers were). However, a non-native speaker editor/reviewer may pick on you, telling me that “Section V” is not a human with a brain to present something to the readers. What should you do then? Give in.

2. Methodology（方法）

To describe the methods and datasets used in the paper, we can (and should) use the present tense.

For example: We use the WOA (World Ocean Atlas) data as initial conditions for our numerical experiments. We use satellite data to validate model’s phytoplankton field in the surface layer.

别跟审稿人“一般见识”：我的一个同事被审稿人“教导”说，这些地方统统必须用过去式！You may say “Fxxx off. This is MY paper！” But, you should only say it to yourself loudly (or quietly). One should choose one’s battle, so let this one go. （不要为小事跟审稿人争。在这里用过去式无伤大雅。）

If you describe how you collected the data（过去式，已经发生了）, however, you have no choice but to use the past tense.（观测数据采回来了，一定是今天以前做的事。对不起，必须用过去式。）

If you describe the procedure of processing the data, however, you may choose to use the past tense (emphasizing how you did it，用过去式，因为你已经处理了这些资料), or the present tense (illustrating how such a procedure should be performed，用现在式，示范如何常规地处理这些资料).

3. Results（结果）

Figure 5 (or Table 3) shows x, y, and z. (一定用现在式，因为作者现在是在与读者实时对话。)

We use the present tense to describe all our (finished numerical) experiments. If you prefer to use the past tense, it is fine as long as you do so consistently. （可以用现在式、或过去式描述你的数值模拟结果。）Do not switch from the past tense to the present tense randomly. （不能太任性哦：一会儿现在式、一会儿过去式。）

Exceptions (不能任性的地方):

To study present (modern day) climate, using the present tense is the ONLY way to go, I am afraid. （如果是研究现代气候，一般用现在式。）

For example: Figure 3 shows （现在式）that Typhoon Megi (2015) moved （过去式）away from the coast suddenly.

如果你不喜欢这种“混合式”，可以这样玩：

Typhoon Megi (2015) moved （过去式）away from the coast suddenly (Fig. 3).

4) Discussion and Conclusions

You may use the present perfect tense, such as “we have shown,” or use the past tense. Just be consistent. （任性的时候到了！但是，认准一个时态，不要朝三暮四哦。现在完成式、过去式都可以。）

Once again, you may use mixed (say past and present) tenses in one sentence.（一个句子中的时态不必统一。）

For example: In this paper, we showed （过去式）that the new index is （现在式） capable of tracking algae blooms in spring.

I hope this brief walk through helps. （后会有期。）

Based on my old Blog of

http://blog.sciencenet.cn/blog-306792-657146.html

和任胜利老师: 科技写作时态 (Past tense? Present tense?)

ps. You may also want to check out my Blog on

Scientific Writing for Beginners (1)-(8)

using this link:

http://blog.sciencenet.cn/home.php?mod=space&uid=306792&do=blog&id=432195