When you're deep into genealogical research, you will probably run across a few individuals with the same name. Are they related? Possibly, but not necessarily. How do you sort them out? The "by guess and by gosh" method can really lead you astray. I have seen family trees with authors who have done just this – one person actually wrote "I just KNOW these people were from Delaware," and are therefore her relatives. No no no no.
I have two Thomas Cains in my line, father and son. The trouble is, there was at least one other person by that name, in that place at that time. Figuring out who's who was a tough job.
Here is a strategy that worked for me:
Make a chart (your word processing program probably has a "tables" feature, or you can do this by hand) with columns for date, locale, event, source, notes and conclusion. Then list the various instances of your name of interest down the left-hand column. Record every piece of information you have relating to that name. After entering it all, sort the items into approximate chronological order. With marriage records, note the names of witnesses or sureties; in probate records, list the names of witnesses and the executor or administrator, as well as heirs. Death certificate informants, owners of adjoining land -- if you know these names, include them.
Was Joseph Fisk appointed county commissioner in 1855? Did someone by that name make a will which was probated in 1846? Oviously these are two different people.
Indicate, when known, whether the person signed a document or marked it with an "X." If the name "Josiah Whitaker"(for example) is signed by the witness to a will in 1789, and the same name appears with an "X" in place of a signature on an 1810 document, it is hardly likely to be the same individual.
Is the name Joseph Fisk shown in the 1850 census, with wife Eliza and six chidren? Is the same name recorded with the designation of "infant" in a probate record for William Fisk in 1848? This would mean the latter was a minor and could hardly be the same individual who had a large family in 1850. (OK, he could have married a widow with six children, but it's a stretch.) Neither could he have been a county commissioner if he was still under age seven years later. In fact, persons in such responsible positions were generally well past their 21st year.
When you have arranged these pieces of information relating to your name of interest, take a hard look at them. Do the events take place in the same or nearby localities? (Remember county and even state lines were not always rigid, and people living near the borders of one political division may have conducted business, been married, or been buried, in an adjoining one.) Are the same non-family surnames cropping up on some documents but not others?
Add to your list, rearrange it, and go back to it time and again. You may solve one question of identity right away, but other issues may not even become apparent until later.
The term "infant," as shown above, is one of the many terms in legal documents which can trip you up. Another is "cousin," which has five definitions in the dictionary "A to Zax," by Barbara Jean Evans. It helps to know the terminology!