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.
Example:
We can write off that accrued liability.
The bond holder is able to determine the terms.
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.
Example:
My neighbors have been able to purchase some real estate.
We will be able to attend the shareholders' meeting.
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.
Example:
George was able to augment his inventory of capital goods by buying in quantity during the previous fiscal year.
Sabrina was able to use her job last summer to save enough money for a down payment on a car.
'Could' and 'was / were able to' are also used to express a general ability in the past in the positive and negative forms.
Example:
He was able to protect his personal assets by setting up the business as a limited liability company.
The bank could issue a voting share report when it was still a savings and loan.