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?
Is the contractor able to continue work on the house while the homeowner is awaiting your reply regarding financing?
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.
Clients can go over their assets and liabilities in the credit counseling session.
We are able to adjust our lending rates.
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.
Our clients will be able to use a credit or debit card to complete their transactions.
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.
We were unable to clinch the commercial account deal with the oil company.
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 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.