Could vs. Should

'Could' and 'should' are past tense modal verbs. In this lesson, we will learn their uses and differences.

What Is Their Main Difference?

The main difference between 'could' and 'should' is that 'could' is used to make offers while 'should' is used to give orders.

'Could' is one of the most commonly known modal verbs. It is used to show past abilities, possibilities, requests, etc. To put it simply, 'could' is the past tense of modal verb 'can.' For instance:

Could you open the window?

Here, we are requesting something.

I could stay up all night back then.

Here, we are talking about past abilities.

'Should' is a modal verb. It is used to make suggestions, show possibility, give advice, predict the future, etc. 'Should' is the past tense of modal 'shall.' Have a look:

They should arrive soon.

Here, we are talking about possibilities.

You should call and apologize.

Here, we are giving advice.

Similarities

Giving Advice

We use 'could' and 'should' to give advice.
'Could' is used to express our disapproval of something that has already happened in the past.
'Should' is used to express our thoughts on an event that may be happening now or will happen in the future.
Take a look at the following examples:

You could study more so you wouldn't fail.

You should study more so you wouldn't fail.

Possibilities

We use 'should' and 'could' to show something is likely or expected to happen. For example:

They could be here soon.

They should be here soon.

Negation and Question

To make sentences with modal verbs negative, we add 'not' to them as shown below:

Could → Could not → Couldn't
Should → Should not → Shouldn't

Here are some examples of negative sentences with 'should' and 'could:'

I could run fast. → I couldn't run fast.

I should have said it. → I shouldn't have said it.

When creating interrogative, we simply invert the modal verbs. Watch:

You should always be this rude. → Should you always be this rude?

I could call him. → Could I call him?

With Other Modals

We can use modal verbs with other verbs but we cannot have more than one modal verb. Take a look at these incorrect examples:

I ~~shall~~ ~~could~~ swim.

I ~~should~~ ~~would~~ leave.

With Conditionals

'Could' and 'should' are modal verbs that can also be used as conditional verbs in conditional mood.

	Could	Should
Conditional Type 1	✓	✓
Conditional Type 2	✓	✓
Conditional Type 3	✓	✗
Zero Conditionals	✗	✗

Conditional Type 1

Conditional Type 1 is used to talk about real situations. These situations are considered to have a high chance of occurrence. For examples:

If your dad calls, you should go.

We could watch a movie if you arrive on time.

Conditional Type 2

Conditional Type 2 talks about hypothetical situations that are imaginary and their chance of occurrence are unlikely. These situations are in the present or the future. For instance:

If you win a lottery, you should help a charity.

If you win a lottery, you could help a charity.

Conditional Type 3

The third type of conditionals talks about the past. In this type, we are talking about an imaginary past that could have happened but it never did. In other words, we are imagining a different past. We can use 'could' in this type of conditional.

If I had practiced harder, I could have won the contest.

I could have been there on time if I had left sooner.

Differences

Past Abilities

We use 'could' to talk about abilities, talents, or skills that we had in the past but we no longer have them or stopped practicing them or the person who possessed the talent is deceased. Have a look:

My grandmother could twirl a pen.

She could do a handstand before she broke her wrist.

Expressing an order

'Should' is used to express a not so strong and polite order, obligation, or instruction. We use it to politely tell other what to do and what not to do. For example:

Everyone should hand in their electronic devices.

You should pay the intuition fee as soon as possible.

Making offers

'Could' is used to make not so definite suggestions. The receiver may or may not accept the offer. Here are some examples for clarity:

Could I be of any assistance?

I could get us snacks on my way to your place.

Future Predictions and Expectations

We use 'should' to predict and estimate a future event. We also use it to express our expectations about a situation. Look at these example:

It should be raining in London right now.

Here, we are expressing expectations.

The bus should arrive any moment.

Here, we are predicting a future event.

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