Can / Could / Be Able to

Follow these structures to form a sentence with can.
S = Subject
QW = Question Word

Follow these structures to form a sentence with to be able to.
S = Subject
QW = Question Word

Present Ability and Future Ability in grammar refer to how we express someone's current or potential capacity to do something. Present Ability describes what someone is capable of doing now. Future Ability describes what someone will have the capacity to do later.

Skill refers to the ability to do something well that has been learned through practice, training, or experience. Skills are developed over time and demonstrate competence or expertise in a particular area. Unlike natural ability, skills are acquired and can be improved through deliberate effort and repetition.

Unusual Ability refers to exceptional or remarkable capabilities that are uncommon or surprising, often expressed using be able to to emphasize the extraordinary nature of the ability. This structure highlights abilities that are beyond what is typical or expected. The phrase be able to is often preferred over can when describing these special capabilities because it adds emphasis to the unusualness of the ability.

Verbs of Senses are verbs that describe what we perceive through our five senses: sight, hearing, smell, taste, and touch. They describe our sensory experiences. With verbs of senses, we typically use can because these refer to natural, immediate perceptions rather than learned abilities.

Theoretical Possibility with can refers to using can to express what is potentially possible or conceivable, rather than actual present ability. This form of can expresses general possibility or potential occurrence rather than someone's specific ability to do something. Theoretical possibilities are based on logic, theory, or potential rather than actual evidence or certainty.

You can use could as well. It is less certain (depends on the person).

Permission/Prohibition with can refers to using can and can't to give or deny permission in informal situations. Can grants permission, while can't expresses prohibition. This usage of can is commonly used in everyday conversation to establish what is or isn't allowed.

Requests with can and could refer to using these verbs to ask someone to do something for you. Can is used for informal, direct requests, while could is more polite and formal.

Offers with can refer to using can to volunteer help or suggest doing something for someone else. This structure is used to propose assistance or services. Offers with can are friendly and direct ways to show willingness to do something for another person. Could in offers suggests possibility rather than certainty, making the offer sound more considerate and giving the other person more comfortable space to accept or decline without pressure.

We use can to say that something is possible or allowed, or that somebody has the ability to do something. We use can to talk about skills (learned abilities).
Be able to is also possible, but can is more usual. It's a good idea to use be able to to talk about unusual abilities.

Past Possibility/Ability with could refers to using could to express what someone was generally capable of doing or what was possible in the past. This form indicates that the ability or possibility existed in the past, whether or not it was actually used or occurred in specific instances.

Permission/Prohibition in the Past refers to using could and couldn't to express what was allowed or not allowed in the past. Could indicates past permission, couldn't expresses past prohibition. These structures describe rules, regulations, or permissions that existed in the past but may be different now.

Could with sense verbs indicates that the sensory perception was possible or actually experienced in the past, describing what someone was able to perceive through sight, hearing, smell, taste, or touch at that time.

Past Skills refer to using could to describe competencies that someone possessed in the past through learning or practice. This structure expresses skills that were developed and maintained over time. Could with past skills indicates that someone had acquired and retained these abilities in the past, whether or not they still possess them today.

Past Ability with was/were able to refers to using this structure to express successful completion of specific actions or achievements in the past. Was/were able to emphasizes that someone actually accomplished something on a particular occasion, this form highlights actual success or achievement rather than just general past ability, indicating that the person not only had the capability but also used it effectively to accomplish a specific goal.

We use could as the past form of can to say that something was possible or allowed, or that somebody had the ability to do something in the past. We use could to talk about skills (learned abilities).
Was/were able to is also possible (see the table).

If we need to express ability in the future, then the appropriate forms of be able to, manage to or succeed in must be used. Ability in the Future refers to using will be able to to express what someone will be capable of doing at some point in the future. Will be able to indicates that the ability doesn't exist now but is expected to develop or become available in the future through learning, practice, or changing circumstances.