This article considers issues arising from ‘system-internal’ reform proposals—proposals which aim to (partly) address investment law’s legitimacy crisis by influencing changes in arbitral reasoning so that investment arbitration is undertaken in more acceptable ways. The key techniques for arbitral reasoning which the internal-reform literature advocates greater use of are analysed. I argue that there are important insights to take away from most of the proposals made. I also highlight where internal-reform proposals have the potential to lead into disagreement or exacerbate the existing legitimacy crisis. I suggest that going forward arbitral-led reform will need to work in a complementary way with wider diplomatic-led reforms, and consider what this interaction may look like. In short, improved arbitral reasoning has a role to play in reforming investment law but is not a complete substitute for broader efforts to work through the divisive issues surrounding the future shape of this regime.