Evaluate the credibility of primary and secondary sources, build an evidence-based thesis, and analyze cause, effect, sequence and correlation

Learning goal: Examine the credibility of primary and secondary sources of information; develop a thesis and use evidence to support or refute a position; and analyze cause, effect, sequence and correlation in a historical event, including multiple causation and the difference between long-term and short-term causal relations. The case used throughout is the explosion of the USS Maine in 1898 and the war with Spain that followed.

Primary and secondary sources. A primary source was produced by someone who took part in or witnessed the events, or was created at the time: a letter, a diary, a photograph, a newspaper report written that week, a government record, a court transcript. A secondary source is an account by someone who was not there, built by interpreting primary sources, usually later: a textbook, a historian's book, a documentary. What sorts a source is its relationship to the events and to the question, not its date alone. A memoir written forty years afterward by a sailor who survived the explosion is still a primary source, though his memory may have faded; a writer in 1898 who only summarized other people's reports was not a witness, and is better evidence of what was being said than of what happened. The category depends on the question being asked. A 1950 history of the Spanish-American War is a secondary source about 1898, but it is a primary source for the question "How did Americans in 1950 remember that war?"

Credibility is examined, not assumed. Neither kind of source is automatically trustworthy. Historians test each one with the same questions. Who produced it, and were they in a position to know? When was it made, and how long after the event? Why was it made, and for what audience? What does it claim, and can those claims be corroborated by other independent sources? They also weigh the author's qualifications and reputation, the author's perspective and bias (including any use of stereotypes), and whether the source's argument is accurate and consistent from beginning to end. A source can be highly credible on one point and weak on another. A newspaper reporter in Havana is a good witness to the sound of an explosion, and a poor witness to what caused it.

The case. On the night of February 15, 1898, the American battleship Maine exploded and sank in the harbor of Havana, Cuba, then a Spanish colony in the midst of a war for independence. More than 250 members of its crew were killed. Within days, several New York newspapers, above all William Randolph Hearst's Journal and Joseph Pulitzer's World, ran headlines and drawings suggesting that Spain had destroyed the ship. These papers were competing for readers, and their sensational style came to be called yellow journalism. A United States Navy court of inquiry reported in March 1898 that an external mine had set off the ship's forward magazines; it did not say who placed a mine. A 1911 board that examined the raised wreck also concluded there had been an external explosion. In 1976 a study directed by Admiral Hyman Rickover concluded that a fire in a coal bunker next to a magazine was the more likely cause. Later investigations have not settled the question.

Applying the credibility test. The newspaper headlines are primary sources for what readers in 1898 were told and for the mood of the press. They are weak evidence for the cause of the explosion, because the papers printed accusations before any investigation and had a commercial motive to excite readers. The 1898 court of inquiry is a primary source produced by trained officers who examined the wreck, which adds credibility, but it worked quickly, under public pressure, with the diving technology of the day. The 1976 study is a secondary source that reanalyzed primary evidence with later engineering knowledge; it has the advantage of distance and the disadvantage of working from records rather than from the wreck as it lay in 1898.

Theses and evidence. A thesis is a claim that can be argued, that answers a historical question and that evidence could support or refute. "The Maine exploded in 1898" is a fact, not a thesis. "The explosion of the Maine was the main cause of the Spanish-American War" is a thesis. Historians develop a thesis from the evidence, then test it: they gather evidence that supports it, and they look deliberately for evidence that would refute it. A strong thesis survives that search, is modified by it, or is abandoned.

Cause, effect, sequence and correlation. A sequence is the order in which events happened. A cause is something that helped make an event happen; an effect is what followed because of it. Sequence alone does not prove causation: that one event came before another is necessary for a causal claim, but not sufficient. A correlation is a pattern in which two things change together: both rise, both fall, or one rises as the other falls. Suppose a historian found that newspaper circulation and public calls for war both rose in early 1898. That correlation would be worth investigating, but it does not by itself show that the papers caused the demand for war; both may have responded to the same news from Cuba.

Multiple causation and long- and short-term causes. Most historical events have several causes. Long-term causes build over years and make an outcome possible; short-term causes are closer in time and help trigger it. For the war with Spain, long-term causes include American economic interests in Cuba, especially sugar; sympathy for the Cuban independence war that began in 1895; reports of the suffering caused by the Spanish policy of forcing rural Cubans into guarded camps; and a growing argument, made by the naval writer Alfred Thayer Mahan among others, that the United States needed a strong navy and overseas bases. Short-term causes include the publication on February 9, 1898, of a private letter by the Spanish minister Enrique Dupuy de Lôme that insulted President McKinley, and the explosion six days later. Congress declared war on April 25, 1898.

A worked model of a thesis tested against evidence. Thesis: "The Maine explosion caused the war." Supporting evidence: the sequence (explosion in February, war in April) and the press campaign built around the slogan about remembering the Maine. Refuting or complicating evidence: the Cuban war and American concern had been building since 1895; McKinley pressed Spain on Cuba before the explosion; and the Navy report never named Spain as responsible. Revised thesis: "The explosion of the Maine was a short-term trigger that turned long-running economic, humanitarian and strategic pressures into a declaration of war." The revision is stronger because it accounts for all the evidence, not only the evidence that fits.

The misconception to avoid. Students often treat primary sources as true because they were "there," and secondary sources as opinion. Both are evidence that must be examined. A primary source can be mistaken, biased or deliberately misleading, and a careful secondary source can correct it.

Worked sourcing: Source: the front page of William Randolph Hearst's New York Journal of February 17, 1898, headlined "Destruction of the War Ship Maine Was the Work of an Enemy" and showing a drawing of a mine under the ship (the page is widely reproduced; work from a reproduction, not from this description). Who: a commercial newspaper competing for readers. When: two days after the explosion, before any investigation had reported. Purpose and audience: to sell papers to a general public. Claim: an enemy, by implication Spain, destroyed the ship. Corroboration: none available at the time; the Navy court reported in March and named no culprit. Conclusion: credible evidence of what the public was being told; not credible evidence of the cause.

Worked sequence and causation: Put in order: Cuban independence war begins (1895); de Lôme letter published (February 9, 1898); Maine explodes (February 15, 1898); Navy court reports an external mine (March 1898); Congress declares war (April 25, 1898). Label each: the 1895 war is a long-term cause; the letter and the explosion are short-term causes; the court report is evidence that shaped opinion but named no one; the declaration is the effect. The skipped step is asking whether each earlier event actually contributed, not merely came first.

Worked correlation: Suppose a student finds that in early 1898 the cities where yellow newspapers sold most copies also sent many petitions calling for war. Correlation: both were high in the same places. Possible explanations: the papers persuaded readers; people who already favored war bought those papers; or both reflected large urban populations. To test the causal claim, the student would need evidence of opinion before and after the papers' campaign, for example letters, editorials in other papers or petitions dated before February 15.

Source record: For four sources on the Maine (a yellow newspaper front page, the 1898 Navy court report, the 1976 Rickover study, a modern textbook), work from a reproduction or excerpt of each that your teacher supplies or that you find in a library or archive collection, and write a full citation for it (title, author or publisher, date, and where you found it). Then complete a table with columns: primary or secondary; author and position to know; date relative to the event; purpose and audience; main claim; what it is credible evidence of; one other source that corroborates or contradicts it.

Independent performance: Write a thesis-driven paragraph of 250–350 words answering "Why did the United States go to war with Spain in 1898?" Success criteria: the thesis is arguable and stated in the first sentence; it names at least two long-term and one short-term cause, each with a date; it cites evidence that supports the thesis and at least one piece of evidence that complicates it; it names one correlation and explains why it does not by itself prove causation; and it states the credibility of each source it relies on in a phrase.