What is the difference between "lest", "just in case" or "in case"?

Question

Oxford dictionary states that lest is synonymous with in case.

Meanwhile, I am too confused about the following. I am wondering when/where would you rather use these? And are they really interchangeable?

• just in case
• in case
• lest

I need an inclusive answer please.

I have looked up dictionaries and I came across different types of definitions and synonyms, especially in the Oxford dictionary, which I provide in a link:

• Oxford's definition on lest
• Oxford's definition on (just) in case

Answer 1

When using "in case" as in "take this umbrella, in case it rains", you acknowledge the possibility of the action (i.e. rain). You're not certain it will happen, but it's not unlikely. You'll often see "in case" in instructions, rules, etc. - for example, "in case of fire, stop, drop, and roll".

When using "just in case", on the other hand, you emphasise the unlikeliness of the action. If you're "taking this umbrella, just in case it rains", you don't really expect it to rain, but you're taking precautions. It's also less formal, it's not something you'll see on a warning sign or in a rulebook.

"Lest" is somewhat poetic and archaic, but I think it puts a bit more emphasis on the undesirability of the consequences than the actual likelihood of the event. Don't quote me on that, though.

Answer 2

The word just in just in case is superfluous. Oxford Advanced American defines it. Mind it, it's an idiomatic use.

(just) in case (…) - because of the possibility of something happening

So, you may get rid of that confusion and consider that in case = just in case

Now, the word lest. It is, as described in Oxford Dictoinary, same as in case but if you see the usage, you'll understand in which context it's used and mean in case. When the word lest is used, it gives a bit flair of fear. So, when in case, it's all about fear, lest seems a preferred choice.

Examples from other dictionaries support this -

worried lest she should be late - from MW Dictionary.

She was afraid lest she had revealed too much - from OALD

he was alarmed lest she should find out - from Collins

So to conclude, in case is almost same as just in case and lest is also in case but when you want to include the element of fear. Merriam Webster defines lest as for fear that.

Also, they are interchangeable if in case is just in case and includes an element of fear. Otherwise, they are not always interchanged. I'd prefer saying, "Take these coins as a change, (just) in case you may need." I'm simply giving the change in case that person requires it. He has money and without those coins, he won't get stuck. But for the convenience, I am giving him the change to use in metros and cabs.

On the other hand, I'd use lest when I want to include the fear element. I may say, "she sat up late worrying lest he be murdered on the way home."

Answer 3

"In case" means "if <something> happens" or "if <something> is true". "In case" is formal English, and is used seriously and straight-forwardly. "In case" is short, so it is a good phrase to use as part of instructions that you need people to read and understand. For example, a fire alarm might have a label saying "In case of fire, break glass."

(I use <angle brackets> to show where you should substitute something into an example.)

The example does not say what to do if there is not a fire. The example implies that you should not break the glass until there is a fire.

"Just in case" means "only if <something> happens" or "only if <something> is true". The extra word has several effects:

• It makes the phrase worse for giving short, easily understood instructions.
• Therefore, "just in case" is usually not used for formal commands.
• Therefore, "just in case" is less formal than "in case".
• "Just in case" explicitly says that the "thing to do" (or "way to prepare") is not useful if the "case" does not happen.
• If "just in case" is used straight-forwardly, it implies that the "thing to do" (or "way to prepare") is usually not very useful.
• Because "just in case" is redundant and informal, people use it jokingly. Often, the joke is that the "thing to do" (or "way to prepare") is really important, or something that you should do anyway.

"Lest" means "to avoid the case" or "to prevent the case". Often if you do something before a problem happens, you can prevent the problem. Therefore, "before" is sometimes a synonym for "lest".

"Lest" is very formal. "Lest" is not used very often, and is becoming archaic. Here are some typical uses of "lest":

• "Lest we forget" is used in speeches and essays about warnings we can learn from history. It is usually used by politicians, and by people writing opinion essays in newspapers. After "Lest we forget," the politician will tell either a short story from history, or the warning.
• "Lest you make a mistake, <do some double-checking>."
• "Lest you go off half-cocked, <consider another possibility>" could be changed to "Before you go off half-cocked, <consider another possibility>" without changing the meaning. This is because if they consider the other possibility, they will find their mistake. After they fix their mistake, they will either not "go off", or they will be prepared to "go off".

A person who "goes off half-cocked" is unprepared in a way that is dangerous to themselves. This is an old saying, about old guns. I imagine a person carrying a gun that is half-way ready to fire, before the person has a chance to aim.