Shall vs Should
The basic difference between “shall” and “should” is that “should” is the past tense of “shall.” But when we use these words or modals, the usage is not as simple as using “should” in place of “shall” in the past tense. “Should” is not used in the past tense independently; it has either present or future reference when it predicates a main clause. “Should” is the conditional form used for “shall.” Occasionally it is used as a past tense of “shall.” To understand the difference, we need to first understand what “modals” are and how they are used.
“Should” is used as deontic modal as well as epistemic modal. Modals are helping verbs. They are also called modal auxiliary. They have varied meanings and are used to convey these varied meanings. “Should” is specifically used to express advisability. Other uses of modals are: ability, possibility, probability, permission, necessity, and requesting assistance, making conclusions, giving instructions and making suggestions, showing preference, making offers, making promises or predictions.
Deontic modals are verbs which are used to give permission and, hence, affect a particular situation. For example, You should go only after you finish the work. Here, permission is being given by the speaker.
Epistemic modals are verbs which show the opinion of the one who is speaking. For example, He should be here any moment now. Here the speaker is not sure but is expressing his opinion.
Meanings and usages
“Should” expresses that some action is correct for someone. For example, You should get more sleep.
It expresses probability. For example, You should have reached the office by now.
It expresses consequences and conditions. For example, Should he have any problems, I will be there to help.
It is used in place of “would,”used mainly with “we” and “I.” For example, I should like to meet her parents.
Expressing somebody’s views from the past about the future. For example, It was decided from the start that the school should be used to educate underprivileged students.
It is used to make harsh words more polite. For example, I should expect you to apologize now.
Shall has slightly different usages and meanings.
Meanings and usages
“Shall” means something that is intended to take place in the future. For example, He shall be the CEO of the company by next year.
It expresses determination. For example, I shall overcome all the hindrances in my way.
It expresses certain laws and rules. For example, The government shall declare an emergency.
For formal writing, “shall” is used to express the future tense.
1.“Shall” and “should” are both auxiliary verbs but have different usages and meanings.
2.“Should” in general English is used as a past tense of “shall” but the usage is occasional. Independently, “should” is not used in the past tense.
3.“Shall” is used more in formal writing than “should.”