shall vs should

Question

This question is not a duplicate of:

• How to choose between shall and should?

• Modal verbs in reported speech

• Usage of 'shall' in questions

because it provides detailed dictionary definitions, reveals a likely contradiction in the strength of these two words, and covers usage scenarios that are not addressed by those questions.

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The definitions of shall and should confused me. It seems that shall can be either stronger or weaker than should.

Case 1: shall < should

• shall:

  • modal verb (SUGGEST)

    used, with "I" or "we", to make a suggestion:

    Shall I call him tomorrow?

• should:

  • modal verb (DUTY)

    used to say or ask what is the correct or best thing to do:

    Should I apologize to him?

Case 2: shall > should

• shall:

  • modal verb (CERTAINLY WILL)

    used to say that something certainly will or must happen, or that you are determined that something will happen:

    You shall go to the ball, Cinderella.

• should:

  • modal verb (PROBABLE)

    used to show when something is likely or expected:

    You should find this guidebook helpful.

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So if two senior people (for example, a shall boss and a should boss) tell me:

• You shall do something. and You should do something., or

• The work shall be done tomorrow. and The work should be done tomorrow.

How can I tell who has a stronger will?

Answer 1

As it clearly states in the definitions that you provide, shall used to SUGGEST something is only used with I/we:

shall I call him tomorrow? - suggestion

So, in the shall/should boss sentences, shall can only mean CERTAINLY WILL. Context would dictate whether should means DUTY or PROBABLE, but whatever the meaning, it is weaker than CERTAINLY WILL.

The shall boss is the tough cookie.

Answer 2

The fact that you find seemingly contradictory definitions should tell you that you're probably misinterpreting the data. Shall has a number of uses, mostly to imply an order or a requirement.

You shall write your grandmother a thank-you note. (I'm telling you to do this)

Should has a number of uses, mostly to imply an expectation or a possibility.

You should write your grandmother a thank-you note. (it's the expected thing to do).

There are other uses. In a question, both can express invitation or suggestion. In this case shall is slightly more formal, and possibly more common in certain dialects:

Shall/Should we go join our friends?

What shall/should we order for dinner?

In any case, if your boss tells you shall do something, take it as a direct order. If they instead say you should do something, treat it as an expectation. Naturally, the "strength" of these depends on context. Some bosses like to make suggestions rather than give orders, but that doesn't mean you are free to ignore them.