The word begin is most appropriately used when referring to the onset of an activity or process in a more abstract, inceptive, or formal context. It is often associated with the early stages of non-physical processes such as events, eras, or experiences.

The term start is commonly used to describe the commencement of a more specific or tangible activity. It is suitable for situations involving physical actions, including beginning machinery or a task, and is also the preferred term in informal settings.

To sum up, begin and start are usually interchangeable, yet begin is generally preferred in more formal or abstract contexts while start is more common in informal situations and with physical activities. Begin tends to imply the initial stage of a process, particularly in non-physical or conceptual matters. In contrast, start often refers to the action of initiating something concrete or functional, such as a device or event. Knowing when to use each word can add a subtle layer of precision to your communication.