Moral dumbfounding occurs when people defend a moral judgement even though they cannot provide a reason in support of this judgement. It manifests as an admission of not having reasons, or the use of unsupported declarations (“it’s just wrong”) or tautological reasons (“because it’s incest”) as justifications for a judgment. It typically occurs for harmless taboos. It is cited as evidence for intuitionist or dual-process theories of moral judgement over rationalist approaches, however the phenomenon remains poorly understood. We test a conflict in dual- processes explanation of moral dumbfounding, where moral dumbfounding is an example of conflict between a habitual response (making a judgement) and a response that results from deliberation (providing a reason for the judgement). One prediction of this explanation is that under specific manipulations (e.g., cognitive load), responses should vary in predictable ways. The dumbfounding paradigm involves three possible responses: (a) providing reasons for a judgement (System 2/deliberative); (b) accepting the counter-arguments and rating the behaviour as “not wrong” (System 1/habitual); © a dumbfounded response (System 1/habitual). Cognitive load manipulations have been shown to inhibit deliberative responding. We present 4 studies in which dumbfounded responding was investigated under cognitive load manipulations. We hypothesised that rates of providing reasons would be reduced under cognitive load. The identification of reasons was inhibited in Studies 1 and 3, but not in Studies 2 and 4. The results do not provide strong evidence that moral dumbfounding be explained as conflict in dual-processes. Future research should investigate this further, addressing methodological limitations identified.