Speaking about Abilities
Can - Be Allowed to
'Can' is used to ask for and give permission. In the simplest sense, we use 'can' to request something. However, at other times 'can' expresses permission to do something specific. 'May' is also used in a more formal sense. In American English, 'May I ...' is considered the correct formal form to ask for permission.
'To be allowed to' can also be used to ask for and give permission. This form is more formal and is commonly used for rules and regulations.
Examples of Asking Permission
Can I use the commercial equipment without training?
Are we able to proceed with the paperwork while we are awaiting your reply on the rate type?
Can - To Be Able To
'Can' is commonly used to express the ability to do something. This usage is similar to the form 'to be able to do something'. Both these forms are acceptable, although 'can' is more commonly used.
Jim can explain what the accrued liability is.
The manager is able to transfer his liquid assets to a personal account.
To Be Able To - Future and Perfect Forms
There is no future or perfect form of 'can'. Use 'to be able to' in all future and perfect tenses.
We will be able to attend the shareholders' meeting.
We will be able to limit our personal risk by becoming a limited liability company.
Special Case of the Past Positive
Use 'was / were able to' when speaking about a specific event in the past in the positive form. Both 'can' and 'to be able to' are used in the past negative to speak about specific events.
Many leading banks were able to reduce their lending rates.
He was able to complete the requirement without involving human resources.
'Could' and 'was / were able to' are also used to express a general ability in the past in the positive and negative forms.
He was able to rely on savings banks in the past.
The mortgage amortization could have been discounted during its first five years.