Co-development aims to ensure the alignment of business processes and support technical systems. During co-development stakeholders need an early understanding of the potential impact of different requirement choices on the enterprise. An early impact analysis understanding is more likely to actively engage stakeholders, highlight strategic options and deliver useful and sustainable systems. However, when multiple stakeholders are involved with differing backgrounds, experiences and frequently competing goals it is inevitable that conflicts occur during the early phases when requirements tend to be opaque. This paper puts forward a conceptual framework for co-development to support collaborative reasoning and decision-making through the modelling of requirements alternatives and arguments, promoting critical reflection, negotiation and discussion.