Lecture: Unit 86 - If... not and unless; If and whether

This lecture covers the usage of if... not and unless, as well as if and whether, as detailed in Unit 86 of the provided file.

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1. If... not vs. Unless

The words unless and if... not are often interchangeable, but there are some situations where one is preferred over the other.

• Interchangeable Use: In many cases, you can use either one to express a conditional statement with a negative condition.

  • Example: "Unless alternative sources of funding are found, the research will not be able to continue." This can be rewritten as: "If alternative sources of funding aren't found, the research will not be able to continue."

• Situations where unless is preferred:

  • When the conditional is a long, complex clause.

  • When the condition is an exception to a general rule.

• Situations where if... not is preferred:

  • In questions.

  • With if only....

  • When expressing a wish or regret.

  • In formal contexts, such as academic writing.

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2. If vs. Whether

The choice between if and whether is generally based on the type of clause and the level of formality.

• When to use whether:

  • In a subject clause: Whether he can swim or not is not the point.

  • After a preposition: He asked me about whether I knew the answer.

  • Before a to-infinitive: We didn't know whether to stay or go.

  • Before or not: We didn't know whether or not he had arrived.

• When if or whether can be used:

  • As an object of a verb: He asked me if/whether I knew the answer.

  • In questions.

In general, whether is preferred in more formal writing and when there is a clear alternative or an or not clause.