Unable means lacking the power, skill, resources, or capacity to do something. When you're unable to reach the top shelf, you physically can't get there without help. When a student is unable to attend class because of illness, circumstances prevent them from showing up.

The word points to a real limitation or barrier. Someone who is unable to solve a difficult equation lacks the knowledge or skill to do it. In contrast, someone who simply doesn't feel like trying has made a choice rather than facing a genuine obstacle. Being unable to swim means you haven't learned how yet. Being unable to lift a heavy box means it exceeds your strength.

The word often appears with “to” plus a verb: unable to finish, unable to remember, unable to decide. Sometimes circumstances make us unable to do things we normally could. A pianist with a broken hand becomes temporarily unable to play. A family might be unable to afford a vacation this year.

Recognizing when people are truly unable to do something matters. It helps you see when someone might need help, more time to learn a new skill, or a different approach. Being unable isn't the same as being unable forever; it describes a situation right now, which can often change with time, practice, or support.