This month, my Scientific American column explored the dawn of rental software such as Adobe Photoshop CC. You can’t buy it; you have to pay by the month or the year to use it. (CC stands for Creative Cloud, but it didn’t take unhappy customers to come up with alternative acronyms like Credit Card—and Cash Cow.)

It is, to be sure, a complicated shift away from the “pay once and own it” model that’s been in place for years. Herewith: some of the most frequently asked questions.

And their answers.

So wait. These new programs are called Creative Cloud. Does that mean I have to be online to use them?
Although Photoshop, Illustrator and the other Adobe programs are no longer sold on a disc, you still install them on your computer (via download)—just as you do with many software programs these days. They run fine when you’re offline.

They do, however, check in with Adobe every 30 days to make sure you’re still a paid-up subscriber. If not, you’re locked out. (One chief benefit of the new rental plan—to Adobe, anyway—is to stifle software piracy.)

Can I rent Photoshop only for a couple months a year, whenever I need it?
Yes, but you pay more per month that way. The $30 monthly plan lets you stop and start as needed. If you’re willing to commit for an entire year, you pay $20 a month instead.

I’m paying only $10 a month for Photoshop CC. Why are you reporting that it costs $20 or $30 a month?
If you owned a previous version of Photoshop, Adobe offers a special rate: $10 a month if you commit to paying for the entire year (that is, $10 off the regular rate). However, this is only a teaser rate—like those used by internet or cable TV providers—good for one year; after that, your price goes up to $20.

How do I know Adobe won’t raise the rates once I’ve started subscribing?
You don’t. Adobe can change the rental rates at any time.

I don’t want to pay a monthly fee. Why can’t I just keep using my existing version of Photoshop? It still works fine.
A: Well, you can—for awhile.

Adobe’s programs, however, are especially susceptible to incompatibility with new versions of Windows and Mac OS X. A couple of years from now they’ll no longer run with the latest operating systems. You’ll be forced to upgrade—or switch.

If you’re a pro photographer, you have another problem: Adobe Camera Raw (ACR). This is the Photoshop accessory program that lets you open RAW files (unprocessed, data-heavy original files captured by your camera’s sensor).

Unfortunately, ACR must be updated for each new camera model. Before long, your existing copy of Photoshop will no longer suffice; you’ll get a new camera and you’ll be unable to open its RAW files.

Even in the days when you could “buy” Photoshop, you didn’t really own it. In the fine print it still said that you were only licensing it. Why the big change now?
That’s true. But that was just a legal distinction; from your bank account’s perspective, you were buying it. That is, you paid once and were allowed to use the software forever (or for as long as it remained compatible with your operating system).

In other words, the rental model still feels to most people like a very different ball game—one that puts the software company in control.