Derivative sources are only used by wayward genealogists who have not seen the light of original sources. A curse on the genealogical research of anyone who uses derivative sources.
A curse on anyone who makes such grandiose statements.
There are times when derivative sources can and should be used. The key, like the key to most things in life, is discernment and deciding when such sources will augment work that has already been done or when they are needed for clarification.
Let’s say that I have the record copy of a will written in 1903 and admitted to probate later that same year. When the will is admitted to probate, the court clerk makes record copy of the will in the will record book. The original will is contained and filed in the packet of loose probate papers.
The original will is the original source. The record copy of the will, while the legal equivalent of the original will is, by most genealogists’ definition, a derivative source because it is a transcription of the original.
The original is what I should use. But let’s say that there are a few words I cannot read on the original. In that case the record copy may contain writing that is easier to read or maybe he was able to read words that I cannot. There are times where using the record copy can help me to interpret the original.
Derivatives are not always bad. This is just one time they can help us to more completely understand an original.