When we speak English, we have all sorts of things we can use to make our meaning clear: stress, intonation, rhythm, pauses — even, if all else fails, repeating what we’ve said.
When we write, however, we can’t use any of these devices, and the work that they do in speech must be almost entirely handled by punctuation.
Consequently, written English has developed a conventional system of punctuation which is consistent and sensible: every punctuation mark has one or more particular jobs to do, and every one should be used always and only to do those jobs.
If your reader has to wade through your strange punctuation, he/she will have trouble following your meaning; at worst, she may be genuinely unable to understand what you’ve written.
If you think I’m exaggerating, consider the following string of words, and try to decide what it’s supposed to mean:
We had one problem only Janet knew we faced bankruptcy
Have you decided? Now consider this string again with differing punctuation:
We had one problem: only Janet knew we faced bankruptcy.
We had one problem only: Janet knew we faced bankruptcy.
We had one problem only, Janet knew: we faced bankruptcy.
We had one problem only Janet knew we faced: bankruptcy.
Are you satisfied that all four of these have completely different meanings? If so, perhaps you have some inkling of how badly you can confuse your reader by punctuating poorly. What is the reader supposed to make of some feeble effort like this?
*We had one problem only, Janet knew we faced bankruptcy.
Bad punctuation does not require an enormous effort to put right. If you work carefully through this course, then, providing you think carefully about what you’re writing as you write it, you will undoubtedly find that your punctuation has improved a great deal. Your readers will thank you for it ever after.