TV crime shows teach us that motive is often the most important piece in solving a mystery. In politics, too, motive is huge.

When they hear about a new political proposal, voters rarely start by studying details. Instead, they ponder motive. If they feel good about the motive, they usually go along with a new idea. If they don't, the details will often be irrelevant.

Politics offers a never-ending supply of examples of success and failure based on perceived or real motive.

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In 1990, Ottawa said a Goods and Services Tax was needed to replace a manufacturing tax that had been silently killing jobs. Voters struggled to buy that. Instead they guessed that this was really about raising more money, which the government adamantly denied. Polls showed that the tax would have been better accepted if the government simply said, "Yes, this will help balance the books." Which, eventually, turned out to be true.

More recently, when B.C. NDP Leader Adrian Dix lost the provincial election, many observers traced his defeat back to the moment he revealed that he opposed both major proposals to move more Canadian oil to Pacific tidewaters. Voters surmised that he was not rejecting projects on their merits, but development in principle. This intuition about his motive stoked fears of the harm New Democrats might do to the economy.

If there's one cardinal rule in bringing forward a new policy, it's this: you must describe clearly and credibly the problem you are trying to solve. Establishing a powerful and believable motive is often much more important than debating the details or finer points.

And so it will likely be with Quebec's new charter of values.

While we've yet to see the actual details of the proposal, there's plenty of debate underway about the motive behind it.

Quebec Premier Pauline Marois seems to think the problem, in a nutshell, is multiculturalism. Apparently "distinct" can be good in some situations, but if everybody starts doing it, not so much.

In reference to England, the Quebec Premier said, "In England, they're smashing each other in the face and throwing bombs because of multiculturalism and nobody knowing any more who they are in that society."

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The Premier argues that what Quebec needs is clear rules, rules that will "bring people together."

So how will voters evaluate Marois's motive, and her charter?

Those Quebeckers who dislike ethnic minority groups will embrace the Marois Charter. Not because of a need for clearer rules, or because they don't know who they are anymore. They will infer a different, darker motive, and will rally behind the proposal.

But I suspect many other voters will resist the charms of the charter. And it will have a lot to do with perceptions of motive.

Buying her stated rationale requires a belief that Quebeckers are staggering around in a cultural zombie state, their value system no longer fully alive but not yet completely dead. So stunned by the religious customs of ethnic minorities that they no longer "know who they are."

There may be some reasonable arguments that can be made for the assurance of secularism in the public sector. But it's truly hard to see the pressing need for this kind of action. Unless, of course, you are a PQ political organizer stressing about the next provincial election.

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And so, whenever Premier Marois says she's trying to "bring people together," lots of voters will hear something else. Something more like I'm "trying to pit one group against others."

The words and the substance of the charter, when revealed, should be scrutinized carefully and fairly. But if history is any guide, the political debate will continue to revolve around motive.

In how she tables the charter proposal, the Premier faces a choice. If she sticks with the script she's been using, she will simply confirm the suspicion that her true motive is political and divisive.

To do better, she must make a much, much better effort to persuade people of the gravity of the problem she is trying to solve, and the reasons why her measure will unify rather than divide her province.

Bruce Anderson is one of Canada's leading pollsters and communications strategists. He is a member of the CBC's popular At Issue Panel, a regular Globe blogger, and a founding partner of i2 Ideas and Issues Advertising.