Modal and Semi-modal Verbs 

Modal and semi-modal verbs serve various uses in English. Here's a categorized list to help clarify their functions.

Modal and Semi Modal Verbs Functions

Obligation

• Must: Expresses strong obligation or necessity.
• Have to: Indicates external obligation or necessity.
• Should: Suggests a duty or recommendation.
• Ought to: Similar to "should," indicating duty or recommendation.

Suggestion

• Should: Suggests a course of action or recommendation.
• Ought to: Suggests a desirable action or course of behavior.
• Could: Proposes a possibility or alternative.

Warning

• Must: Conveys a strong necessity or requirement, often for safety or rules.
• Should: Advises against a particular action or behavior.
• Ought to: Warns against a potential negative consequence.

Ability

• Can: Expresses present ability or possibility.
• Could: Expresses past ability or possibility.
• Be able to: Indicates ability or capacity.

Permission

• May: Indicates permission or possibility.
• Might: Suggests a possibility or seeks permission.

Certainty

• Must: Conveys strong certainty or necessity.
• Shall: Expresses a strong assertion or intention.

Habitual Actions

• Used to: Describes past habitual actions or states.

Modal and Semi-modal Verbs in Use

Obligation

• Must: "You must submit your assignment by Friday."
• Have to: "I have to attend the meeting tomorrow."
• Should: "You should apologize for your mistake."
• Ought to: "He ought to help his parents with the chores."

Suggestion

• Should: "You should take a break and relax."
• Ought to: "We ought to consider all the options before making a decision."
• Could: "You could try the new restaurant downtown."

Warning

• Must: "You must not enter this area without permission."
• Should: "You should not play with fire."
• Ought to: "She ought to be careful while driving at night."

Ability

• Can: "I can speak Spanish fluently."
• Could: "She could lift the heavy box with ease."
• Be able to: "He will be able to finish the project on time."

Permission

• May: "May I borrow your pen?"
• Might: "I might leave work early today."

Certainty

• Must: "She must be at home by now."
• Shall: "We shall overcome this challenge."

Habitual Actions

Used to: "I used to play the piano when I was younger."

Possibility

• Can: "It can be challenging to learn a new language."
• Could: "She could be at the library studying."

Logical Assumption

• Must: "He must be the new employee everyone is talking about."
• Should: "The package should have arrived by now."

Prohibition

• Must not: "You must not smoke in this area."
• Cannot: "Visitors cannot enter the restricted area."