The present poster discusses the role of the famous Quinian bootstrapping learning process in the acquisition of mental state terms such as happy, believe, pain, etc. At first, the poster characterises Quinian bootstrapping in which the so-called placeholder structure plays an important role. The placeholder structure consists of symbols whose meanings are initially learned in terms of each other. Later, the placeholder structure is infused with meanings via the so-called modelling processes. A modelling process can be analogical mapping, abduction, induction, etc. Susan Carey (2009) introduced Quinian bootstrapping in her explanation of the acquisition of numeral list representation and rational number as well as certain aspects of intuitive physics. Second, I apply this well-known learning mechanism to the acquisition of the meaning of mental terms. I distinguish between three stages in the learning of the semantics of mental words. The present poster will characterise the three stages in detail.