Are you writing fiction or blog posts? Is Microsoft Office Word telling you contractions are a problem? Incomplete sentences are a problem? And other things that are stylistic choices you're free to make as a writer are problems?
No, the rules of writing haven't changed. It's just that Office is now set for academic writing, not any old kind of writing (Why do they think there's only one kind of writing?!), but you can fix this issue. I found solutions online, but they weren't very helpful, probably because they were for older versions of Word. This solution is for the latest version (although it's possible it might be good for slightly older versions, as well).
Here's how you can fix this problem: The next time you see that pesky green line under your beautiful words, right-click it and then click "grammar" in the pop-up window. That will open this screen:
|(Please don't try to read the words under the window in this screen grab. They contain several huge spoilers for Why It Still Mega Bites, the second book in the Legend of Gilbert the Fixer, and you don't need that.)|
See where it says Options at the bottom left? Click that. The next screen should open with"Proofing" highlighted in the left-hand column. In the pop-up menu to the right of that, scroll down to where it says "Writing Style: Grammar & Style" and click the "Settings" button next to it. That will give you the "Grammar Settings" menu shown here:
Go through the options and unclick the things you don't want to be corrected on, like fragments and run-ons, contractions, sentence fragments, sentences beginning with and, and so on. Then click "Okay." This will take you back to the previous menu.
Near the bottom of the menu on the right, you'll see "Exceptions for." Click to open the drop-down menu and select "All New Documents" and then click "Okay" at the bottom of that menu.
And that's it. Yay! You've made those pesky green lines go away!