The Merriam-Webster dictionary defines "a theory" "as a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena." It goes on to further define "a theory" "as an ideal or hypothetical set of facts, principles, or circumstances!" Ok…don't panic! No one will ask you to define Einstein's theory at this point. But when it's all about developing a theory on an ancestor, just remember what Joe Friday use to always say in past episodes of Dragnet, "Just the facts ma'am."
I always say that a family researcher is like being a good detective! A good detective will figure out a crime by conducting a lot of research and then attempt to figure out what happened. The detective will then generate a theory as to how that crime occurred and then go about proving that theory correct. It is possible that in the research the initial theory is incorrect and then it may be necessary to redefine that theory and search in another direction. This could help lead to a totally different but successful conclusion. A family historian can also research an ancestor that same way. As a family historian, your job is to find information on your families based on "just the facts!"
There will be times in your research when many of us hit that brick wall in which we will not be able to find anything on a particular ancestor. Despite the hours of research already conducted, your research might very well come to a halt. For many of us, myself included, going any further on that family will seem hopeless. Many of us at that point, just give up thinking that it's hopeless. It doesn't have to be that way. Drawing a theory on that particular ancestor might help you change the direction of your research which then could lead you to other records. Perhaps that could be enough to break down that wall in your search.
Start with what you already know and have been able to confirm. The more documents that you have to confirm a theory, the more confidence you have to verify the theory. In short, if Aunt Martha claims that Great Grandma O'Leary was born in Kilkenny, you need more than her word. Although Aunt Martha might be able to lead you in the right direction from your interview with her or her written notes, it's still important to verify that from either a civil record or a baptismal record from the church.
I always write those facts down on a sheet of paper or on your laptop or tablet. I like to use a timeline when developing a theory about a particular ancestor. You can keep it simple by just putting the ancestors name on top of the page and leave room for the date of the event, next the event then the location the event took place.
You might find that you overlooked a particular time frame in that ancestor's life. The timeline will give you to see where your ancestor has been during that person's life and perhaps what record and time frame you need to concentrate on in your research. This will also aid in developing your theory on where that ancestor originated or where that ancestor might have lived during a particular time frame.
Mark down on the timeline all the information you have on this ancestor. Be sure to also mark down where you found this information especially if you need to recheck that record sometime in the future. This will give you an overview of what you already know and what you might need to further search. This will also help you in refining your theory. "I know that great grandpa was born in Ireland in the 1830s and was in New York in the New York State Census of 1865."
Perhaps your great grandpa left for America prior to the Civil War as many young men from Ireland did in the late 1850s. Your theory then could be that "Great grandpa O'Leary immigrated to the U.S. in the late 1850s." You might have more than one theory about that particular ancestor. Now, check what records would be available including passenger lists, the National Park Service's Soldiers and Sailors database, or even the U.S. Census record from 1860. There are plenty of other records that are available online.
There are many online records here in the U.S. and even around the world that are now online thanks to the internet. That number continues to climb everyday. The age of digitization can assist you in finding out some of the answer you are looking for regarding an ancestor. Even if you have been on a particular web site recently, check again. Many new records are being digitized and are showing up on these web sites on a regular basis. So, if you haven't been on a site for more than a month, check again and see if new information is now on that web site.
The theory along with the data backcheck could help you locate that piece of information regarding the ancestor that you've been missing all this time. Still haven't found anything on this ancestor? You then might have to refine that theory by changing the dates or even broadening the theory a bit.
A theory or theories about an ancestor will help you refine and narrow your search. This which will allow you to pinpoint specific records from the time period of your theory. Researching ancestors can be overwhelming at times, especially if you get stuck and don't know where to turn. A Theory about an ancestor can aid in defining what part of your research you need to concentrate on and where you should limit your search. Defining a theory on an ancestor is one tool that can give you a way to work around that "brickwall!"