“Chronological reasoning” means thinking logically about how and why the world changes — or, sometimes, stays the same — over time. While all fields of knowledge offer arguments based on evidence or make comparisons, historians are uniquely concerned about the past and its relationship to the present. How is the world different now than it was 50 years ago, 500 years ago, or 5,000 years ago? Why did the world change? How have some aspects of the world remained relatively the same over long periods of time? On what basis do historians simplify the long and complicated past by breaking it into smaller eras?

Historical Causation Causation has to do with explanations about how or why changes take place in history. Sometimes there is an obvious connection between an event and its consequence, like a cue ball striking the eight ball and making it move. And some events are fairly straightforward: the attack on Pearl Harbor prompted President Roosevelt to ask Congress for a declaration of war against Japan. But even this seemingly simple example soon becomes more complicated. Why did Japan attack the United States? What role did the American embargo on the sale of oil have on Japan’s decision? Why did the United States enact this embargo? All of these other events took place just a few years before the Pearl Harbor attack. If we go even further back, we’ll gain additional insight about the larger context of the Japanese government’s decision. A longer-term analysis might lead, for example, to an understanding of Japanese imperial aggression as an outgrowth of their rapid industrialization during the Meiji Restoration of the late nineteenth century.

Just as there were many factors behind the attack on Pearl Harbor, most examples of historical causation involve multiple causes and effects. Events and processes often result from developments in many realms of life, including social, political, economic, and cultural. Historians cannot test these in laboratories the way scientists can, but they can use historical evidence and reasoning to determine which of these are probable causes and effects. Historical causation also involves large processes, complex causes, unintended consequences, and contingencies, as the chart above describes.

You can begin to develop the skill of determining causation by asking yourself, whenever some significant change in history is described, what reasons explain the development. If the answer seems simple, keep digging, because there’s bound to be a more complicated (and longer-term) explanation.

Patterns of Continuity and Change over Time Historians are interested in both historical changes and persisting patterns, or “continuities.” Change is easier to see: when one country conquers another one, that event often becomes part of the historical record. But some things stay relatively the same for long periods of time. Because continuity (such as a network of trade that remains in existence for hundreds of years) is less dramatic than change, it can be harder to spot.

What counts as continuity depends on the scale of time you’re working with. The Soviet Union was continuous throughout most of the twentieth century. However, in the time frame of Russia’s history since the formation of Kievan Rus in the ninth century, the Soviet era looks more like a short-lived exception to tsarist rule.

When historians talk about continuity, they’re not implying that a particular pattern applied to everyone in the world or even in a particular country or region. Nor are they claiming that absolutely nothing changed in the pattern they’re describing. For example, agricultural production has been continuous for thousands of years. But there are exceptions to this broad statement: on the one hand, some people have continued to be foragers; on the other hand, methods of farming have changed substantially with technology. So the continuity of agriculture is a generalization but not a completely unchanging pattern or a pattern that applies to everyone on the planet.

To work on developing this skill, look for places in your text where the authors directly indicate that a historical pattern persisted over time and explain why that pattern persisted. But even when an author focuses on change in history, you can still find continuity by inference, since few things ever change completely. When the text describes a new development, ask yourself what didn’t change. For example, employing the ideas of the European Enlightenment, Thomas Jefferson in the Declaration of Independence proclaimed “that all men are created equal.” But many of the thinkers of the early republic used custom and biology to justify limiting suffrage to white men only. In this way, they continued to defend traditional stereotypes about the inferiority of women and non-Europeans that had existed for centuries.

Periodization Periodization refers to the ways that historians break the past into separate periods of time. Historians look for major turning points in history — places where the world looked very different before some event than it did after — to decide how to break the past into chunks. They then give a label to each period to convey the key characteristics and developments of that era.

Because the past is complex, any attempt to create eras and give those eras labels can provoke disagreement. For example, the word Renaissance, which means “rebirth,” was first used in the later sixteenth century by the Italian art historian Giorgio Vasari to describe artists such as his contemporary Michelangelo whom Vasari regarded as geniuses even greater than those of the ancient world. Over time, the word’s meaning was broadened to include many aspects of life, expanded geographically to include developments in many countries, and extended chronologically to include several centuries. But scholars do not agree about when exactly the Renaissance began and when it ended, and they debate whether certain artists and writers should be considered “Renaissance” figures. Many note that along with significant changes during the Renaissance, there were also striking continuities with the medieval period that preceded it. Others have questioned whether the word Renaissance should be used at all to describe an era in which many social groups saw decline rather than advance. These debates remind us that all periodization is done by people after the fact, and it all involves value judgments. No Delaware or Shawnee soldier in the Ohio Valley in the mid-eighteenth century, for example, knew he was fighting what would later be called “The French and Indian War,” or that he was living in a period of time that would later be referred to as “colonial America.”

As you develop this skill, pay attention to the labels for various periods that are used in the chapter you’re reading. Sometimes chapter titles themselves contain a period label, which can give you an idea of what the authors have decided is the main story for that era. Chapter 3, for example, is titled “The British Atlantic World,” and Chapter 25 is titled “Cold War America.”