Scotland does not have a government yet, although a step towards the formation of an administration was taken yesterday when the SNP struck a deal with the Scottish Greens to work together at Holyrood. But a new lexicon is already evolving to describe and define the new political era. The phrase confidence and supply has achieved a cachet at Holyrood and among observers of the parliament without an administration. It is a product of proportional representation in the electoral process and has a habit of resulting in coalition or minority government. Scotland is heading towards the latter option, with Alex Salmond as First Minister.

Under a confidence and supply agreement, the minor party supports the majority partner in the event of a vote of confidence in an administration lacking a majority and in the vote on its budget (the supply element). These are, broadly, the two areas where a vote, going the wrong way for an administration, can bring it down. Confidence and supply can be a comfort or reassurance for the major partner seeking to push through its policies. For the minor partner, the agreement can give an enhanced opportunity to advance its agenda.

The SNP-Green deal is not strictly a confidence and supply agreement. It will ensure that the two Green MSPs will vote for Mr Salmond as First Minister. This should ensure his appointment if, as expected, the Scottish Liberal Democrats and Conservatives abstain in the vote. In return, the Nationalists will endorse a climate change Bill as an early priority and nominate a Green MSP to chair a Holyrood committee (under the rules they have too few MSPs to chair a committee in their own right).

Will this looser arrangement work, or will it be a recipe for instability? It does mean that the Greens cannot join Labour in a minority coalition administration, effectively Jack McConnell's last hope of forming a government, given the decision of the Liberal Democrats not to jump into bed with his party again and the refusal of the Scottish Conservatives to coalesce with anyone. There are policy areas where the SNP and the Greens could rub along nicely together but there are others where they are poles apart, notably transport. Mr Salmond has to pay a price for securing the support of the two Greens but he must not allow the tail to wag the dog, especially on projects such as the M74 extension that are vital for the economy but which the Greens oppose.

Mr Salmond suggested inadvertently another addition to the lexicon earlier this week when he said that the SNP would have to be nimble of brain and light of foot to govern effectively at Holyrood. The neophyte Nationalists will have to be that and more if they are to pass the test of government.