People use analogies to create mental models that they can apply to infer from familiar to new situations (Collins and Gentner 1987). According to structure-mapping theory (Gentner 1983), an analogy is a mapping of knowledge from "a familiar concrete domain (the base or source)" into "a less familiar or abstract domain (the target)," when the relational structure that applies in the source can be applied in the target (Gentner and Smith 2013). This means that when recognizing commonalities between the source and the target, the analogy can prompt inferences helping to comprehend the target domain. The mapping does not depend on specific content of the source and the target. It establishes a structural and attributive alignment between the domains, while structural relations have priority over object attributes (Gentner 1983; Gentner and Smith 2013). In other words, analogy does not require that corresponding objects in the source and in the target resemble each other, but they must hold a matching system of relations (relational structure). Researchers considered two levels of analogies: surface analogies that strike the eye and deeper analogies referring to inner relations and processes (Harrison and Treagust 1998; Bonnardel and Marmèche 2004). They noted that deeper analogies have greater impact on learning and recommended to guide students to identify and use such analogies. Gentner (1983) emphasized the value of surface similarities for attracting attention to the analogy and motivating its further exploration. Though analogical reasoning is regarded as an "inherent quality of human reasoning" (Goswami 2013, p. 14), it is subjected to the level of learners’ prior knowledge of the source domain, the ability to focus on relations between objects rather than on objects themselves, and the capacity to process and manipulate multiple relations simultaneously (Wilbers and Duit 2006; Gentner and Smith 2013; Richland et al. 2006).