難度：進階
你有多少次聽過：過去式代表過去發生的事，現在完成式代表過去發生，但後果延續至今的事？不過，這跟研究論文的前言有什麼關係？以前發現的結果跟我眼前的論文有關係嗎？
困惑嗎？很多人都這樣覺得，底下是簡單的指引。
現在完成式
現在完成式經常用來廣泛陳述領域的趨勢。Recently（近來）或long considered（長期以為）等時間形容詞，還有gather attention（引起關注）和draw criticism（招來批評）等字眼，往往是表達現在完成式，原因是事情的發生時間不確定，或者說，這非事件而是趨勢。
正確：The contribution of agricultural production to greenhouse gas has long been debated.
（中譯：農業生產助長溫室氣體的爭論歷久不衰）
正確：Recently, the idea that some crops leave larger CO2 footprints than others has gathered attention.
（中譯：近來，某些作物二氧化碳足跡甚於其他作物的觀念引起關注）
正確：Some researchers have argued that crops that require heavy use of nitrogenous fertilizers, such as potatoes, leave a larger CO2 footprint than crops that require less, such as legumes.
（中譯：有的研究人員主張，馬鈴薯等氮肥下得較重的作物，二氧化碳足跡甚於蔬菜等用量少的作物）
這方面的現在完成式用法，包含——特定時點的——日期以括號表示的場合：因為日期不是句型的語法成分。
正確：Some researchers have argued that crops that require heavy use of nitrogenous fertilizers, such as potatoes, leave a larger CO2 footprint than crops that require less, such as legumes (2002).
﹝中譯：有的研究人員主張，馬鈴薯等氮肥下得較重的作物，二氧化碳足跡甚於蔬菜等用量少的作物（2002）﹞
簡單過去式
研究的日期若顯示於句子正文，就必須用過去式；事實上，用現在完成式會非常奇怪。
正確：Smith et al. conducted a 2-year field experiment in 2009 and 2010 in rice paddies to learn about the connection between rice production and greenhouse gases emissions.
（中譯：Smith等人在2009和2010年在稻田做過2年期的田間實驗，以便了解稻米產量和溫室氣體排放的關聯）
奇怪：Smith et al. have conducted a 2-year field experiment in 2009 and 2010 in rice paddies to learn about the connection between rice production and greenhouse gases emissions.
（中譯：Smith等人2009和2010年在稻田在做2年田間實驗，以便了解稻米產量和溫室氣體排放的關聯）
於Introduction段落，過去式通常適用於特定作者之名字被引用時。
正確：Smith et al. conducted a 2-year field experiment in rice paddies to learn about the connection between rice production and greenhouse gases emissions.
（中譯：Smith等人在稻田做過2年期的田間實驗，以便了解稻米產量和溫室氣體排放的關聯）
正確：Bouwmann et al. (2002) argued that crops that crops require heavy use of nitrogenous fertilizers, such as potatoes, leave a larger CO2 footprint than crops that require less, such as legumes.
（﹝中譯：Bouwmann等（2002）主張，馬鈴薯等氮肥下得較重的作物，二氧化碳足跡甚於其他用量少的蔬菜作物）
說明：留意Bouwmann et al.若以some researchers代替，如前例，用的是現在完成式，原因是some researchers不確定，但Bouwmann et al.相當明確。
同理適用下筆者；we（我方）或the author of the present study（本文作者）是特定的研究人員，是以應該用過去式報導己方的發現結果。
正確：We previously conducted an experiment to learn about the carbon footprints for various crops grown in Taoyuan County (2011).
﹝中譯：我們之前做過實驗，以便了解桃園縣境內各種作物的碳足跡（2011）﹞
否定句型
現在完成式比較常見於否定的語法時態（即用到not），特別是用到investigated（探明）、determined（確定）、revealed（顯露）等動詞的場合。
正確：Whether reducing potato crops is a viable strategy to reduce greenhouse gas emissions has not yet been determined.
（中譯：尚未確定減少馬鈴薯作物是減少溫室氣體排放的可行策略）
考量有些事情從來不曾探明，也就是根本找不出特定時間：比較A polar bear was born in the zoo yesterday（中譯：動物園昨天有隻北極熊誕生）和A black polar bear has never been found.（中譯：從未發現過黑色的北極熊）
也就是說，簡單過去式比較適合特定日期或將作者寫進句子的情況。
正確：Smith et al. conducted a 2-year field experiment in rice paddies to learn about the connection between rice production and greenhouse gases emissions. However, they did not consider the effects of nitrogenous fertilizers.
（中譯：Smith等人在稻田做了2年期的田間實驗，以便了解稻米產量和溫室氣體排放的關聯，不過他們未考慮氮肥的效果）
總結：
- 現在完成式用在句子未寫出明確日期或作者的情況。
- 現在完成式用來表示趨勢或未有定論。
- 除此之外用過去式。
Download Tip Here: 
用在前言的現在完成式和過去式
Uni-edit English Writing Tip 006: Present Perfect Tense and Past Tense in your Introduction
Difficulty: Advanced
How many times have you been told the following: “the past tense denotes an event that happened in the past, while the present perfect tense denotes an event that happened in the past, which has present consequences.”? But, what about the Introduction section of research papers? Aren’t all of the past findings relevant to my present research?
Confused? So are we! Here is an easy guide.
Present perfect
Present perfect is often used for broad statements about trends in the field. Temporal adjectives like “recently” and “long considered” and words like “gather attention” and “draw criticism” often suggest the present perfect tense. This is because these events did not occur at specific point in time: rather, they are trends.
Correct: The contribution of agricultural production to greenhouse gas has long been debated.
Correct: Recently, the idea that some crops leave larger CO2 footprints than others has gathered attention.
Correct: Some researchers have argued that crops that require heavy use of nitrogenous fertilizers, such as potatoes, leave a larger CO2 footprint than crops that require less, such as legumes.
This usage of present perfect includes cases where the date—a specific point in time—is expressed in parentheses: because the date is not a grammatical part of the sentence.
Correct: Some researchers have argued that crops that require heavy use of nitrogenous fertilizers, such as potatoes, leave a larger CO2 footprint than crops that require less, such as legumes (2002).
Simple past
When the date of a study is expressed in the body of the sentence, past tense is necessary. In fact, present perfect sounds unnatural.
Correct: Smith et al. conducted a 2-year field experiment in 2009 and 2010 in rice paddies to learn about the connection between rice production and greenhouse gases emissions.
Unnatural: Smith et al. have conducted a 2-year field experiment in 2009 and 2010 in rice paddies to learn about the connection between rice production and greenhouse gas emissions.
In the Introduction Section, past tense usually applies when the specific authors are referenced by name.
Correct: Smith et al. conducted a 2-year field experiment in rice paddies to learn about the connection between rice production and greenhouse gas emissions.
Correct: Bouwmann et al. (2002) argued that crops that require heavy use of nitrogenous fertilizers, such as potatoes, leave a larger CO2 footprint than crops that require less, such as legumes.
Explanation: Notice that when “Bouwmann et al.” was “Some researchers” in the Present perfect explanation above, it was present perfect. This is because “some researchers” is not specific, whereas “Bouwmann et al.” is specific.
The same principles apply to you: “we” or “the authors of the present study” are specific researchers, so past tense should be used to report findings of your past studies.
Correct: We previously conducted an experiment to learn about the carbon footprints for various crops grown in Taoyuan County (2011).
Negative sentences
The present perfect is more common when the grammatical tense is negative (i.e. when “not” is used.) This is especially true with verbs like “investigated”, “determined”, “revealed”, etc.
Correct: Whether reducing potato crops is a viable strategy to reduce greenhouse gas emissions has not yet been determined.
Consider that if something has never been investigated, there is no specific time when it was not investigated: compare “A polar bear was born in the zoo yesterday” with “A black polar bear has never been found”.
That being said, again, the simple past is more appropriate if the specific date or authors are written in the sentence.
Correct: Smith et al. conducted a 2-year field experiment in rice paddies to learn about the connection between rice production and greenhouse gas emissions. However, they did not consider the effects of nitrogenous fertilizers.
To sum up:
- Use present perfect when the specific date or authors are not written in the sentence.
- Use present perfect to denote trends or lack of conclusions.
- Use past tense otherwise.
Download Tip Here: Present Perfect Tense and Past Tense in your Introduction
END OF TIP