Traditional View:
* 4 Progressive Forms: This is the most common understanding. We focus on the present and past tenses, along with the active and passive voices.
* Present Progressive (Continuous): I am *walking*.
* Past Progressive (Continuous): I was *walking*.
* Present Perfect Progressive (Continuous): I have been *walking*.
* Past Perfect Progressive (Continuous): I had been *walking*.
Wider View:
* More Forms: You could argue for more forms if you include:
* Future Progressive: I will be *walking*.
* Future Perfect Progressive: I will have been *walking*.
* Conditional Progressive: I would be *walking*.
* Conditional Perfect Progressive: I would have been *walking*.
Further Considerations:
* Passive Progressive: While less common, you could argue that forms like "I am being *helped*" are also progressive.
* Modal Verbs: You might even include modal verbs like "I might be *walking*" as a type of progressive.
Conclusion:
The "number" of progressive verb forms depends on your definition and level of detail. The traditional view recognizes four, but you can broaden it to include more based on your perspective.