The ego is described as having three bodies, the gross, the subtle and the causal, but that is only for the purpose of analytical exposition. If the method of enquiry were to depend on the ego’s form you may take it that any enquiry would become altogether impossible, because the forms the ego may assume are legion. Therefore, for the purposes of self-enquiry, you have to proceed on the basis that the ego has but one form, namely that of the ‘I’-thought.