難度：高階
論文的前言和文獻回顧，皆須包含研究的背景。成功發表論文的作者，往往知道如何使用動詞時態，當成有力的說服工具。
舉例如下，文中二個動詞是轉述”結果發現”的慣用格式，第一個動詞有報導的功能（「表示」、「顯示」、「指出」等），而第二個動詞和句子內容有關。現在讓我們來檢視現在式和過去式的差別。
該用哪種動詞時態？
Gupta et al. (2012) show//showed the lower vitamin D levels in children with severe, therapy-resistant asthma (STRA) are//were associated with worse asthma control and lung function.
（中譯：Gupta等人（2012）表示，嚴重難治氣喘（STRA）兒童身上的低維生素D水準，和氣喘控制和肺部功能惡化有關。）
第一個動詞：show//showed
推薦用無爭議的過去式，既然是過去的研究，這用法較適當。
正確且自然：Gupta et al. (2012) showed that…
用現在式並非不可：但其意謂此刻發表且公示的「研究」指出……，但可能較不自然，請謹慎使用。
正確但有點奇怪：Gupta et al. (2012) show that…
第二個動詞: are//were associated
用過去式是把”發現結果”指向實驗當時的時間，用現在式則表示”發現結果”的真實且至今適用。兩種時態皆可，但現在式的語氣更強；第二個動詞用現在式給人”發現結果”更肯定的印象！
正確：…lower vitamin D levels in children with STRA were associated with worse asthma control and lung function.
(指向Gupta等人過去研究的發現結果。)
正確且肯定：…lower vitamin D levels in children with STRA are associated with worse asthma control and lung function.
(Gupta等人的發現結果至今屬實。)
你甚至可用相對薄弱的過去式，隱約否定先前的”發現結果”。
Smith et al. (2008) found that Vitamin D levels had no relation with asthma severity or recurrence. However, Gupta et al. (2012) reported a contradictory finding, saying that lower vitamin D levels in children with STRA are associated with worse asthma control and lung function.
（中譯：Smith等人（2008）沒發現低維生素D水準和氣喘嚴重程度或復發的關聯，不過這和Gupta等人（2012）的發現矛盾，後者表示STRA兒童身上的低維生素D水準，和氣喘控制和肺部功能惡化有關。）
(Smith等人沒發現關聯，但其實我們認為有。)
省略前半段（Gupta et al. showed…），好讓轉述”發現結果”的力道更強！讀者從引用即可得知作者所表示的發現結果。
Lower vitamin D levels in children with STRA are associated with worse asthma control and lung function (Gupta et al., 2012).
(中譯：STRA兒童身上的低維生素D水準，和氣喘控制和肺部功能惡化有關（Gupta等，2012）。)
總結：
- Showed、demonstrated，和suggested等轉述型動詞用過去式比較自然。
- 陳述”發現結果”用現在式和過去式皆可：但現在式語氣較強烈。
- 非常堅定的主張甚至可以避用轉述型動詞。
Download Tip Here: 
如何於前言的章節使用過去式和現在式?
Uni-edit English Writing Tip 007: Using Past Tense and Present Tense in your Introduction Section
Difficulty: Advanced
The Introduction and Literature Review sections of your paper must include background to your research. Authors who publish successfully and publish often know how to use verb tense effectively as a powerful persuasive tool.
Let’s take the example below, whose two verbs are a standard format for reporting findings. There are two verbs: the first verb has a reporting function (“to show”, “to demonstrate”, “to suggest”, etc.), while the second verb relates to the contents of the sentence. We will look at present tense and past tense.
Which verb tense should we insert?
Gupta et al. (2012) show // showed that lower vitamin D levels in children with severe, therapy-resistant asthma (STRA) are // were associated with worse asthma control and lung function.
First verb - show//showed
Using past tense for the first verb is uncontroversial and recommended. It is appropriate because the research was conducted in the past.
Correct & Natural: Gupta et al. (2012) showed that…
Using the present tense is not forbidden: it suggests “the study, which is published and available to read at present, says…”. However, it can sound affected: use with caution.
Correct & Slightly Strange: Gupta et al. (2012) show that…
Second verb – are//were associated
Using past tense localizes the findings to the time of the experiment, while using present tense suggests the findings are true and applicable even now. You can use both, but the present tense sounds stronger. Using the present tense for the second verb will be perceived as a strong assertion of the findings!
Correct: …lower vitamin D levels in children with STRA were associated with worse asthma control and lung function.
[This was a finding of Gupta et al.’s study in the past.]
Correct and stronger assertion: …lower vitamin D levels in children with STRA are associated with worse asthma control and lung function.
[This finding of Gupta et al. holds true even today.]
You can even use the relative weakness of the past tense to implicitly dismiss past findings.
Smith et al. (2008) found that vitamin D levels had no relation with asthma severity or recurrence. However, Gupta et al. (2012) reported a contradictory finding, saying that lower vitamin D levels in children with STRA are associated with worse asthma control and lung function.
[Smith et al. said there was no relation, but we believe that, in reality, there is a relation.]
To report findings most strongly, you can omit the first part (“Gupta et al. showed…”) entirely! The readers will know you are reporting a finding because of the presence of a citation.
Lower vitamin D levels in children with STRA are associated with worse asthma control and lung function (Gupta et al., 2012).
To sum up:
- Past tense is more natural for reporting verbs like “showed”, “demonstrated”, and “suggested”.
- Present tense and past tense are both okay for describing findings: present tense is stronger.
- You can even omit the reporting verb altogether for a very strong assertion.