A source can be many different things — a document, an index, a book, even a person or other sorts of materials (such as clothing) in or from which information about specific facts or events relating to one’s family history can be extracted. When evaluating and documenting sources used to establish family connections in your genealogy or family research, it is very important to understand the different types of sources that you will find — their quality and physical importance. Reliable sources become vital elements in the historical research of one’s family. Why? Because each source of information helps you prove that the information you are compiling is not only true but also accurate.

Although a book could probably be written about the information we’ll share in the next few lines, we will make it as brief yet as concise as possible. However, you can follow the links, if you desire more information about any specific type of source.

Original vs. Derivative Sources
All sources are not created equal. It is important that genealogists understand the meanings behind the terms original and derivative, because there are two types of sources and they are, indeed, original and derivative.

When referring to the physical description or properties of a document or record, original sources are records that contribute written, oral or visual information that is not derived from any other written or oral record; they are derived from first-hand knowledge. They are, in fact, the source from which a copy, reproduction, translation, transcript or an abstract is usually derived because they are the first record of their type. An original source, therefore, is most often the original document or recording related to any event or fact that may be in question; However, certain exceptions do exist; it may also be a legible and legitimate image of an original document seen as a photograph, a good quality photocopy, a scanned copy on the Internet or a CD-ROM, or an official copy on microfilm or microfiche like those provided by the NARA for census and military records.

Derivative sources, by their definition, are records which have been derived — hand copied, abstracted, transcribed, indexed or summarized — from previously existing sources. Thus, a derivative source may not retain the same value as the original because as they are copied from one derivative source to the next errors are more apt to be amplified over time.

As a rule,original sources carry more weight than derivative sources.

Primary, Secondary and Tertiary Information
The information provided by the sources we find can be classified as primary, secondary or tertiary information. When referring to the quality of a document or record, we can say that primary sources are the records of choice. Since this type of record was/is created at or near the time of an event by a person who witnessed or had reasonably close knowledge about the event. It contains primary information; and, primary information is information provided from first-hand knowledge of the recorder or the informant.

By contrast, a secondary source, is a record created significantly after the event occurred or by a person who was not present during the event. It is secondary information; and, secondary information is information that was not provided by someone or some thing with first-hand knowledge.

Finally, defining a tertiary source of information for genealogical purposes is often problematic, at best. Typically tertiary sources of information represent distilled information, collected or summarized from other sources. Therefore, we can fairly safely say a genealogical report is a tertiary source of information. This is true in that it contains the culmination and compilation of a variety of information gained from many different sources, both primary and secondary, about a single person or a family. The same would be true for a book written today about one’s noble heritage.

Primary sources always carry more evidentiary weight than do secondary or tertiary sources.

As we gather data from various sources of different types, we use that information to compile evidence, which can be classified as either direct or indirect.

Direct evidence is relevant information that answers a question (whether verbalized or not), such as, “What is my mother’s date of birth?”, “When were my grandparents married?” or “What was my great grandmother’s maiden name?” Therefore, a birth certificate provides direct evidence about someone’s date of birth, a death certificate provides direct evidence about someone’s death and a marriage certificate provides direct evidence about a marriage date as well as the names of the people being married.

Indirect evidence, on the other hand, has relevant data, suggests that other information may be relevant and often implies an answer to a question, but it may need other supporting evidentiary data to form a positive conclusion.

Here’s an example of indirect evidence:
I was searching for a great uncle. When and where was he born? In an old church record, I found the birth but there was no name to confirm this child was my uncle. The listing included the names of my great grandparents, the date of birth, the town where they were living and the reference — “son of the Smith’s.” This baby had not yet been named.
Some time later, I received a letter from another researcher in my family. With her letter, she included a photocopy of my great grandfather’s Bible, where he had written in the names and dates of birth for his children. The date for the uncle I had been looking for was clearly the same as the one I had previously found in the church record. One document (the Bible inscriptions) gave me direct evidence of this Uncle’s birth and by comparing the two documents I gained indirect evidence about where he was born. Finally, about a year later, I found three census records with his year of birth and his state of birth included. These census records provided more indirect evidence suggesting that I had drawn the correct conclusions.

We must analyze the evidence to draw a conclusion. So, the better the sources and information, the stronger the evidence. This in turn leads to more reliable conclusions.

Keep this in mind… as sources are collected, you will begin to see trends — among other data, you notice that dates of birth match as do marriage dates, places of residence and dates of death also match. Then when you DO come across conflicting data (and you will) it becomes much easier to determine the reliability and validity of a newly found source. This is especially true if you know where the rest of your data has been found or you know where it came from. That is why it is so very important to copy down as much information as possible from each and every source as it is located.

Eventually, other researchers may want to verify that certain (or all) assertions you make about people filed within your genealogical records are correct. Those researchers can then use the source information you provide to assess the reliability and validity of what you have recorded, written or said about your ancestors, just like you did when you compiled the information. However, in order for another genealogist to retrace your steps and find the same data you found, you must create an accurate source citation for each and every event or fact you locate about a family member.