How do you compete with free? A taxonomy of reasons to pay for digital files

My latest Guardian column is "In the digital era free is easy, so how do you persuade people to pay?" and it's a first approximation of a taxonomy of reasons to buy stuff that you can download for free from unauthorized sites. I find that discussions about digital sales are often muddied by arguments about whether a particular strategy is good or bad for business, and I hope that by enumerating as many of the selling-propositions as we can and the strategies that complement or undermine them, we can improve the debate:

Buy this because you're supporting something worthwhile

This is the proposition made by indie artists and it's one reason so many major entertainment companies hive off "indie" labels, imprints and brands. Supporting the arts feels genuinely good – knowing that your money is going to someone who made some work that moved you and entertained you. This may be the most powerful motivator of all, but it's also the trickiest.

For this to be really effective, the customer needs to have a sense of the person or people behind the work. That means this proposition favours artists with highly visible, personal public profiles, and not every artist has it in them to hang out there in the world with their audience. Some people are just shy. Some are worse than shy – some artists have negative charisma, and every time they appear in public (physically or virtually), they reduce the business case for buying their works.

The paradox of this proposition is that most high-profile artists got their profile through the good offices and extensive expenditures of a publisher, label, studio or other intermediary. But artists who are backed by these intermediaries are seen as less "worthwhile" than their independent counterparts – after all, the proposition is "support an artist," not "support a giant company that takes most of the money and gives some of it to an artist" (no matter how much the artist may value that arrangement and believe it to be a fair one).

In the digital era free is easy, so how do you persuade people to pay?