A concept proves its force not when it is admired or accurately summarized, but when it survives use. Use transfers thought from the protected coherence of its original text into situations marked by different materials, institutions, scales and conflicts. Weak concepts become slogans; overextended concepts lose their boundaries; strong concepts reveal capacities that were only latent in their first formulation. To use Lefebvre is not merely to affirm that space is socially produced but to examine how zoning, transport, archives or platforms participate in that production. To use Foucault is to identify the rules that make statements and objects institutionally visible. To use Bowker and Star is to trace the consequences of a category once it enters a form, database or standard. To use Habraken is to ask who controls each level of a complex environment and what may change without destabilizing the whole. To use Benjamin is to arrange fragments so that a relation becomes perceptible without being flattened into linear explanation. Application is therefore one of the places where theory is evaluated. Yet use can also strip thought of its resistance, turning difficult concepts into convenient tools. Genuine use allows the concept to alter the problem, complicate the method and sometimes refuse the task assigned to it. Practice tests thought, but thought must also reorganize practice. A field strengthens when inherited concepts are neither preserved in glass nor consumed as disposable language, but repeatedly exposed to consequence.