By Jo Coburn
Political correspondent, BBC News
There has never been any love lost between Tory leader David Cameron and the prime minister's close friend and Schools Secretary Ed Balls.
But their recent spat over the importance of marriage and its role in family policy has marked out the issue as a clear election battleground.
Mr Cameron accused Labour of a "pathological" opposition to supporting marriage after the schools secretary and married father of three said that the institution was not the key to a happy family.
Rewarding married couples and civil partnerships in the tax system has long been Conservative Party policy, as has the commitment to end what the Tory leader calls the "couple penalty" that pays people to live apart rather than together.
Specific proposals by Mr Cameron's predecessor, Iain Duncan Smith, to allow married couples to combine their tax allowances - which would have cost nearly £5bn - have never been adopted as party policy.
That aside, Mr Cameron wants to celebrate and encourage marriage as he says happens in most European countries.
But Mr Balls has hit back, saying the Tory policy is to judge marriage as first class and any other relationship as second class. That, he claimed, was not in the interests of children.
A child's welfare was best protected though stable and lasting relationships between parents.
Political arguments over family policy often end in tears.
Conservative plans to reward marriage will certainly keep the core vote happy, but this is unlikely to be the issue that woos floating voters to their side.
Mr Cameron was given something of a rough ride when he addressed members of the single-parent charity Gingerbread.
He came under attack from one single mum who demanded to know if it was right that she pay more tax because she had not found Mr Right.
But Mr Cameron insisted that government should not remain neutral on the issue of family, although he denied he was at '"war" with single parents.
For the Tories, couples breaking up, absent fathers and divorce all feed into the party's image of Britain as a "broken society".
Recognising that family policy has become a key dividing line, Labour's deputy leader Harriet Harman weighed in and gave a speech on "modern families" last week.
She said there was no evidence that giving a tax incentive supports marriage or keeps people together.
It would, in her words, give tax relief to the man on his third marriage but deny it to his first and second wives bringing up his children.
It would also provide support to people who did not necessarily need it.
But, having discussed these disputes, one striking thing about Ms Harman's speech was that, just like Mr Cameron, it seems to show that Labour believes the family is hugely important and that supporting it is a "public policy imperative at the heart of government."
It is the approach which differs.
Herein lies the problem. While the parties may dispute the best way of keeping families together for the sake of a better society and in a bid to win votes, the public may simply feel that governments should not interfere in the first place and cannot influence the outcome anyway.