Grammatical Features of EST ： Mood
一、Subjunctive Mood
In scientific and technical English，the subjunctive mood is widely used to describe hypothetical conditions. Hypothesis has two types-true hypothesis and false hypo-thesis. True hypothesis express the hope, wish and supposition of the writer. It indicates that the writer thinks that the condition is possible to be fulfilled. False hypothesis indicates that the writer thinks that the condition is unlikely to be fulfilled or it did not happen at all.
1. True Hypothesis
a. Possibility
In this case the hypothetical condition may be fulfilled. This type of hypothesis is used in scientific methods of research. It is used to reach conclusion. Example:
“A farmer has to cross a river one day with a dog, a sheep and some hay. The only boat he has is so small that he can only get one animal or the hay into it besides himself. The farmer knows that the dog is liable to attack sheep and that the sheep cannot resist eating hay. How does the farmer manage to get himself，the animals and the hay across the river safely?
The farmer now has several alternatives. Two of them are expressed in the following hypotheses ：
First hypothesis； the farmer takes the sheep, leaving the dog and the hay together. What will be the consequence?
If the farmer takes the sheep, leaving the dog and the hay together, it will be a safe way.
Second hypothesis： the farmer takes the dog，leaving the sheep and the hay. What consequence can you deduce?
If the farmer takes the dog, leaving the sheep and hay, the hay will be eaten up by the sheep.
The farmer has to cross the river four times. He must take the sheep first. Then he takes the dog，returns with the sheep leaves (he sheep and takes the hay. Finally he takes the sheep and crosses the river again. That will be the safest way.
As can be seen from the above example, hypotheses are provisional explanations which are based on observation and can be tested by further observation. We can show this process as follows ；problem→observations→hypothesis (provisional explanation of relations between facts) →deductions from the hypothesis→evidence for or against the hypothesis→conclusion.
b. General Truths
Examples； If water becomes very cold, it freezes. If ice is placed in the sun，it melts.
These statements without reference to any particular time are true all the time. We use here the Simple Present tense in both clauses of the above examples.
2. False Hypothesis
a. Unlikeness
In this type of hypothesis, although the condition might happen, it probably will not. It is also used when referring to something that we regard as untrue. It is an unreal supposition.
Examples ：
If a researcher performed an experiment (hypothesis), it might (could) be a failure (possibility only).
If all the ice in the world melted (possibility only), the level of the sea would rise about 250 ft (inevitable result).
If I were you, I should not do that. (untrue)
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