如何在英文文章中段落內使用May、Might、Could、Should、Must等助動詞

提問： 「我一直對於要如何使用should、must、can、may、could和might感到很困惑，特別是將這些字用於文章中的討論段落。可否告知這些字之間的差異性，以便讓我可以輕鬆的應用於討論段落內。」

―大學副教授於學術演講後的提問

回答：

本節要探討堪稱複雜的語言範疇：「助動詞」，這在撰寫討論章節時相當重要。在科學寫作中常用的助動詞包括： may、might、could、can、should、ought to、need to、have to 以及 must。此處並不討論未用於正式科學寫作中的助動詞，像是用來表達「允許」的 can 或 may。

助動詞常用來修飾一個句子的「真實價值」。在像：

The drop in pressure was due to a crack in the pipe

一 句中，並未使用助動詞。作者告訴讀者是何種原因造成壓力的下降，並且以具體證據加以證明。然而，如果作者寫的是：

The drop in pressure may have been due to a crack in the pipe

那麼作者就是為壓力的下降提出一個可能的原因。如果寫：

The drop in pressure must have been due to a crack in the pipe

則是表明作者確定是管子破裂導致壓力之下降，但並無確切證據予以證實。確定某一現象為真，和知道某一現象為真，完全是兩碼子事。雖然使用助動詞 must 為句子賦予更多力量，但同時也表達了證據的缺乏。

助動詞在結果與討論中特別有用。在此章節中，作者撰寫和研究結果相關之理由、詮釋與義涵，因此經常需指出某些現象是 :

1. 可能的理由 a possible reason
2. 明顯的詮釋 an obvious interpretation
3. 可能的義涵 a probable implication

以下是從一段結果與討論中摘錄的典型句子：

The kinetics can be described by these equations, suggesting that the electrons are transferred directly. This might involve a supercharge mechanism, but the data could also be described by electron transfer via a hopping mechanism.

為了開始思考這些助動詞有何功能，請利用以下簡短的練習，將 A 欄中的助動詞與 B 欄中的意義加以配對。這些助動詞中，大部分均具有多重意義。

A	B
	可以／能夠 He . . . go home by himself. (He is able to go home by himself.)
Should Must	可能的／可供選擇的 He . . . go home. (It is possible that he will go home.)
Can Ought to	也許／大概 He . . . be home soon. (He will probably be home soon.)
May Could	幾乎可以確定 He . . . be at home. (It is virtually certain that he is at home.)
Need to Might	建議性的 He . . . go home. (I advise him to go home.)
Have to	必須的 He . . . go home. (It is necessary for him to go home.)

 

現在，請對照參考答案：

Can	可以／能夠 (He can go home by himself.)
May Might Could Can	可能的／可供選擇的 (He may/might/could/can be at home.)
Should   Ought to	也許／大概 (He should/ought to be home soon.)
Must Have to	幾乎可以確定 (He must/has to be at home.)
Should   Ought to	建議性的 (He should/ought to go home.)
Must Need to Have to	必須的 (He must/needs to/has to go home.)

 

這些助動詞之所以不易使用，有兩個理由。第一，有些助動詞具有多種意義。因此，當使用如 should 這個助動詞時，請確定所要表達的意義是可能（likely）發生，還是應該發生（advisable）。

其次，大多數助動詞並不遵循標準文法規則。在否定或其他時態中，有些助動詞會消失，有些則會改變語意。例如 He must go home 和 He has to go home 的語意相同，但是 He must not go home 則意指「不准他回家」，和 He doesn’t have to go home 之語意明顯不同。

下表列出這些助動詞在過去式及否定句中的功能，並舉例說明。此表並未探討每一個助動詞的所有可能用法。

1. 能力／用處

現在式	Can	This software can distinguish between different viruses.
現在式 否定	Cannot	Until 18 months a child cannot use symbols to represent objects.
過去式	Could	。It was found that the gun could shoot accurately even at 300 meters.
	Could have	。If we had extended the time period we could have produced more crystals.
過去式 否定	Could not	。In 1990, 80% of households could not receive digital television.
	Could not have	。The subjects reported that they could not have fallen asleep without medication.

 

備註：

• 當用來表示能力或用處時，助動詞 can 只能使用上述兩種時態。如果需要使用其他時態，則需改用 be capable of 或 be able to。例： It is believed that this software will eventually be capable of distinguishing between different viruses.
• Could 意指過去通常有能力／可以完成某事；而 was able to 則用來描述特定的過往事件或場合。例：The result suggests that in this case, the viruses were able to multiply freely. 若無法確定究竟該用 can 或 be able to ，那麼可使用 be able to ，這樣比較保險。

2. 可能性／可採用選項

現在式	May Might Could Can	A rubber seal may/might/could/can be useful at this location.
現在式 否定	May not Might not （但不能使用 Could not 或 Cannot）	A rubber seal may not/might not be useful at this location.
過去式	May have Might have Could have （但不能使用 Can have）	The fall in pressure may have been/might have been/could have been caused by leakage.
過去式 否定	Might not have （但不能使用 Could not have 或 Cannot have）	The fall in pressure may not have been/might not have been caused by leakage.

 

備註：

• 有時候，添加 well 可以用來表達對此可能性有更強的確認性。
• Might 的語氣較 may 弱。
• 有趣的是，can not 和 cannot 的意義截然不同。Can not 的語意和 may not 或 might not 一樣，都是「可能不（possibly not）」，但是除了用在 this can not only damage the sample, it may even destroy it completely 之句子結構外，鮮少運用。反之，cannot 則代表「不可能 impossible」，是完全不同的意思。Could not、cannot、could not have 和 cannot have 都屬於這一類用語。

例句如下：

We realize that this cannot be due to a change in pressure.

We realized that this could not be due to a change in pressure.

We realize that this cannot have been due to a change in pressure.

We realized that this could not have been due to a change in pressure.

作者的意思並非「可能不是」( possibly not )，而是「不可能」( impossible)。

3. 可能性／信服／預期

現在式	。Should   。Ought to	The material should remain stable if it is kept below 30°C.
現在式 否定	。Should not 。Ought not to	The material should not decompose unless heated above 30°C.
過去式	。Should have 。Ought to have	By the time the cobalt is added, the crystals should have dissolved.
過去式 否定	。Should not have 。Ought not to have	This was unexpected; the material should not have decomposed at this temperature.

 

備註：雖然 ought to 語意和 should 相同，但在科學寫作中不常見，因此並未舉例。

4. 幾乎確定

現在式	。MUST 。HAVE TO	Our results indicate that contamination must be due to the presence of sea water in the pipe.
現在式 否定	Cannot	It is clear that contamination cannot/could not be due to the presence of sea water in the pipe.
過去式	Must have	Our results indicate that contamination must have been due to the presence of sea water in the pipe.
過去式 否定	。Cannot have 。Could not 。Could not have	It was clear that contamination could not be/cannot have been/could not have been due to the presence of sea water in the pipe.

 

備註：

• Virtual certainty 之助動詞表示所描述事實不可能有其他解釋。
• Have to 在科學寫作中較不常用，所以並未舉例。
• Must not 意指「不被允許」（not allowed/permitted），並非 not possible。

5.建議／意見

現在式	。Should 。Ought to	The apparatus should be disconnected from the mains during repairs.
現在式 否定	。Should not 。Ought not to	This material should not be exposed to sunlight.
過去式	。Should have 。Ought to have	The apparatus should have been disconnected from the mains during repairs.
過去式 否定	。Should not have 。Ought not to have	This material should not have been exposed to sunlight

 

備註：

• 雖然 ought to 的意思和 should 相同，但是在科學寫作上較少使用，所以並未舉例。
• Should have/ought to have 通常表示某件事並未發生，而 should not have/ought not to have 通常表示某件事確實發生。

6. 需要／義務

現在式	。Must 。Need to 。Have to	The apparatus must/needs to/has to be disconnected from the mains during repairs.
現在式 否定	。Need not 。Do not need to 。Do not have to	The apparatus need not/does not need to/does not have to be disconnected from the mains during repairs.
過去式	。Needed to 。Had to	We needed to/had to heat the valves before use.
過去式 否定	。Did not need to 。Did not have to 。Need not have	。We did not need to/did not have to heat the valves before use. 。We need not have heated the valves before use.

 

備註：

• We did not need to/did not have to heat the valves before use 並未表明我們是否加熱了閥門，而 we need not have heated the valves before use 則顯示我們已進行了加熱處理，但此一處理並非必要。
• Must not 意指「不被允許」（not allowed），而非「不必要」（not necessary）。

 

額外相關閱讀推薦：

1. 助動詞Should、Could與Would之間有什麼差異？
2. 如何區分Could、Might、Should等情態動詞的使用時機？
3. 如何使用to和for？

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