A state's consent may be invalidated if there was an erroneous understanding of a fact or situation at the time of conclusion, which <answer>formed the "essential basis" of the state's consent</answer>. Consent will not be invalidated if the misunderstanding was due to the state's own conduct, or if the truth should have been evident.
An erroneous understanding of a fact or situation may only invalidate a state's consent to a treaty if what is also true about the erroneous understanding?
formed the "essential basis" of the state's consent