Conclusion

You should be aware that all aspects of your speech are constantly going to change as you move toward actually giving your speech. The exact wording of your central idea may change and you can experiment with different versions for effectiveness. However, your specific purpose statement should not change unless there is a really good reason, and in some cases, your instructor will either discourage that, forbid it, or expect to be notified. There are many aspects to consider in the seemingly simple task of writing a specific purpose statement and its companion, the central idea statement. Writing good ones at the beginning will save you some trouble later in the speech preparation process.