Key Difference: ‘Shall’, most commonly, refers to something that a person must to or intends to do. While ‘should’ is used as a past tense of ‘shall’.

‘Shall’ and ‘should’ are interrelated words, in the sense the ‘should’ is the past tense of ‘shall’. However, in many cases, ‘should’, being a modal verb acts differently under certain circumstances. Let’s see the definition of each word in order to better understand its behavior and usage.

Dictonary.com defines ‘shall’ as:

• Something that will take place or exist in the future
• Something, such as an order, promise, requirement, or obligation
• The will to do something or have something take place
• Something that is inevitable
• To be able to
• To have to: must
• An offer, suggestion or request

From this we can see that the usage of the word shall differs according to the context it is used it. Most commonly, shall is used in order to state something a person must do, or will do.

Examples of Shall:

• We shall arrive tomorrow.
• You shall leave now.
• He shall answer for his misdeeds.
• I shall go out if I feel like it.
• That day shall come.
• You shall do as I say.
• Shall we go out for lunch?

‘Should’ on the other hand is commonly considered as a past tense of ‘shall’; however it does not always act as such. ‘Should’ being a modal verb, changes usage depending on the context. A modal verb gives more information about the function of the main verb that it governs.

Dictionary.com defines ‘should’ as:

• Simple past tense of shall
• Used to express condition
• must; ought
• would
• to express futurity from a point of view in the past

Examples of ‘should’:

• If he should leave his father, his father would die
• You should brush your teeth after each meal
• She realized that she should have to do most of her farm work before sunrise
• I should think you would apologize.
• You should not do that.
• People with high cholesterol should eat low-fat foods.
• We should return the video before the video rental store closes.
• I should have started on my paper by now.

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