"Thou canst" is an archaic way of saying "you can". It belongs to the Early Modern English period, and its use has become obsolete in contemporary English. Today, speakers of English use a variety of synonyms to express the idea of capability or permission. Synonyms for "thou canst" include phrases like "you are able", "you have the ability", "you have the opportunity", "you may", "you're free to", "you have the capacity", "you're permitted to", and "you have the power to". These phrases are commonly used in various contexts, such as in job interviews, classrooms, daily conversations, and legal documents.