A centre-left coalition would consist of CDA, at least one of the left-wing parties PvdA or SP and at least one third party. The first option that is being considered is of the three major parties; CDA-PvdA-SP. Since 1958, only two cabinets have been larger than this. Variations may include swapping the SP for either the ChristianUnion or the GreenLeft; or the PvdA for both of these smaller parties. However, there are some problems with this formation: PvdA-leader Wouter Bos and CDA-leader Jan Peter Balkenende were unable to form a two party coalition in 2003, because of personal problems, which are unlikely to have diminished. Over the past half-century CDA-PvdA coalitions have proven to be unstable. Furthermore, both the PvdA and the SP had pointed out during their campaign that the differences between CDA and PvdA have never been so great. Another issue is that in the CDA-PvdA-SP coalition, the largest party (CDA - 41 seats), which has profiled itself as a winner of the election, would be a minority compared to the two left wing parties (together 58 seats). Finally, although the SP has dropped its most extreme plans, it still has large programmatic differences mainly with the CDA but also with the PvdA.