The reasons for this are complex. Periodizing blocks will inevitably overlap, or even seemingly contradict one another. Furthermore, certain periodizing concepts only apply under specific conditions. Some have a cultural usage (but 'the Romantic period' seems to exclude Ingres). Others refer to historical events ('the Inter-War years: 1918-1939'), yet others are defined by decimal numbering systems ('the 1960s', 'the 17th Century'). Others are named from influential or talismanic individuals ('the Victorian era', 'the Edwardian Era', 'the Napoleonic Era').
Similar problems attend other labels. Is it possible to use the term 'Victorian' outside of Britain? It sometimes is used when it is thought that its connotations usefully describe the politics, culture and economic conditions characteristic of the last two-thirds of the nineteenth century. Nevertheless periodizing terms often have negative or positive connotations which may affect their usage. This would include 'Victorian', which is often used negatively to suggest sexual repression, class conflict, heavy industry and so on. Other labels such as 'Renaissance' have strongly positive characteristics. As a result, these terms will sometimes be extended in meaning. Thus the 'English Renaissance' is virtually identical in meaning to the 'Elizabethan Period'. However the Carolingian Renaissance is said to have occurred during the reign of the Frankish king Charlemagne. There is a space of approximately seven hundred years between these two renaissances. Other examples include the 'American Renaissance' of the 1820s-60s, referring mainly to literature, and the 'Harlem Renaissance' of the 1920s, referring mainly to literature but also to music.
Because of these various positive and negative connotations, some periods are luckier than others regarding their names, although this can lead to problems such as the ones outlined above. The conception of a 'rebirth of Classical Latin learning is first credited to an Italian poet Petrarch, the father of the Renaissance, a term that was not coined until the 19th century, but the conception of a rebirth has been in common use since Petrarch's time. The dominant usage of the word Renaissance refers to the cultural changes that occurred in Italy, and which culminated in the High Renaissance at around 1500. This concept applies dominantly to the visual arts, referring to the work of Michelangelo, Raphael and Leonardo da Vinci. Secondarily it is applied to other arts, but it is disputed whether it is useful to describe a phase in economic, social and political history. Most professional historians (defined as paying members of organizations devoted to the propagation of history in higher education, like the American Historical Association) now refer to the historical period commonly known as the Renaissance as 'the Early Modern Period'. There has been no substantive change in the courses taught or books published to correspond to the change in period nomenclature, but this in part reflects differences between social history and cultural history. The timeframe is also slightly different, in that 'Renaissance' tends to refer to events over a much longer and generally earlier period than 'Early Modern'.
The Gothic and the Baroque were both named during subsequent stylistic periods when the preceding style was unpopular. The word 'Gothic' was applied as a pejorative term to all things Northern European and, hence, barbarian, probably first in the generation of Francois Rabelais. The word 'baroque' (probably) was used first in late 18th century French about the irregular natural pearl shape and later about an architectural style perceived to be 'irregular' in comparison to the highly regular Neoclassical architecture of that time. Subsequently these terms have become purely descriptive, and have largely lost negative connotations. However the term 'Baroque' as applied to art (for example Rubens) refers to a much earlier historical period than when applied to music (Händel, Bach). This reflects the difference between stylistic histories internal to an art form and the external chronological history beyond it.
In many cases people living through a period are unable to identify themselves as belonging to the period that historians may later assign to them. This is partly because they are unable to predict the future, and so will not be able to tell whether they are at the beginning, middle or end of a period. Another reason may be that their own sense of historical development may be determined by religions or ideologies that differ from those used by later historians.
It is important to recognise the difference between self-defined historical periods, and those which are later defined by historians. At the beginning of the 20th century there was a general belief that culture, politics and history were entering a new era - that the new century would also be a new era in human experience. This belief was repeated at the beginning of the 21st century, though in a very different way. Other cultural and historical phases have only been described many years, or even centuries, later.
One tactic for Periodization of the distant past, as in Anthropology, is to rely on events, such as the invention of some tool or the origins of language, which are known to exist, but about which little is known in detail.