This document discusses the differences between present and past ability using various ability expressions in English.
For present ability, it explains that "can" and "am/is/are able to" both express ability to do something currently, with "am/is/are able to" implying there may be some difficulties.
For past ability, it states that "could" expresses ability to do something in the past, while "was/were able to" implies there were potential difficulties but the action was still manageable then.
Several examples are provided to illustrate the uses of these ability expressions in the present and past tenses. Readers are then prompted to practice using the expressions in sentences about their own abilities from