Solidarity is a union between two persons. We might think that there is a “giver” (the person that helps a weaker one) and a “receiver” (the weaker person that is helped). But the specificity of solidarity is that each person gives as much as she receives: it is an exchange between a material, financial or moral support and gratitude. It can thereby be defined as a mutual assistance, which is not motivated by common interest. Is it motivated by a feeling or by a sense of responsibility? We will see that solidarity relies on a triangle of thinking, feeling and acting which depends on each person.