In government (public sector) accounting, spending from the treasury cannot begin until the relevant authority has been formally granted. The appropriation bill, once passed, becomes the Appropriation Act, which provides the main legal authority for government ministries and departments to spend money on approved programmes for the year.
Because the legislative process of passing the appropriation bill can take time, government business often needs to continue before it is finally approved. A provisional general warrant is the instrument used to authorise limited, temporary spending during this gap, so that essential government activities are not brought to a halt while the bill is still going through the legislature. Once the appropriation bill is passed, it is superseded by the substantive authority to spend under the Act.
The other warrants operate at different stages: a supplementary general warrant authorises additional spending after the main budget has already been approved and found insufficient; a warrant transfer permits moving an already-approved allocation from one budget head to another; and a reserved expenditure warrant relates to spending set aside for specific reserved purposes. None of these apply before the appropriation bill itself has been approved.
Examination reminder: the word "provisional" is the key clue; it signals temporary authority granted in advance of the appropriation bill's approval, distinguishing it from the other warrants, which all assume the main budget is already in force.