Modal notions play an important role in science. Many scientifically useful predicates are dispositional in nature, and the scientific practice of experiment presupposes the possibility of active intervention in the course of nature. It is therefore interesting to ask which kinds of modality are involved, and how we can best understand them. In this paper we focus on the representation of things in modal contexts occurring in science, and ask which formal methods of philosophical logic are adequate for reidentifying, or tracing, things from case to case. We illustrate the importance of tracing via a discussion of possible experiments in science and in everyday life. After pointing out shortcomings of standard systems of quantified modal logic, we introduce CIFOL, case-intensional first order logic, as a newly established formal framework that helps to elucidate the notion of tracing. We illustrate the framework by discussing the identity of biological individuals with lumps of matter.