Critical thinking is necessary in genealogical research

The use of critical thinking and analysis when doing family history is absolutely necessary. Not using these skills may result in an inaccurate family tree.
People who have critical thinking and analysis skills use logic, mathematics, correlation of records and deduction as well as ask the right questions regarding the source materials to ensure the accuracy of their research.
Using logic, you can assume that parents are older than their children; barring multiple births, children are not born less than nine months apart; women lose their ability to have babies between ages 45 and 55; and before modern transportation, the same person could be in places hundreds of miles apart at the same time.
Mathematics come into play when you do the math relative to ages; birth, marriage and death dates; and the origin of sources. How reliable is the information about people who lived in the 1700s that is recorded in a bible that was printed in the 1920s? Is it possible for a child to be born to a mother who is 3 years old?
Correlating records can go a long way to proving lines, especially in a big city or with a common name. Finding birth, marriage or death records and noting the addresses of the events and then correlating these records with other records such as censuses and city directories can help complete your family picture when no single record is able to prove a relationship.
Asking the right questions helps to clarify the direction you should take your research. Are the parents the correct age to have this child? Are they too old? Too young? Are they living in the expected area or in a place the family has no ties? Do additional records confirm known facts?
Deduction is taking facts and, using the previous skills, coming to an accurate conclusion. A child who is born when a mother is 5 or 65 is probably not the child of that mother. The John Smith who lives for years at the same address as your Mary Smith is probably related somehow. Knowing the common nicknames used in records will confirm that the Ike and Martha you found are probably the same people as the Isaac and Patsy found in other records.
Critical thinking in searching for and acquiring records relating to your family will prove relationships and expand direct lines when just one record won’t do the trick.