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Prepare to Practice Series

Understanding Authority

Understanding authority is foundational to good legal research. This video covers the basics of authority in the federal and California courts. 


Expanding your Research

One-Good-Case Method:

In practice, you'll likely have some "starting point" that is on point for the issue you're researching: a case, a statutory cite, or a regulatory cite. You likely found it through: 

  • Using Secondary Sources

  • Using Annotated Codes

  • Suggestions from supervisors or colleagues

  • Diving right in with a freestyle search (not the preferred method, but we’ll allow it)


Once you have a “good” case, the following tools and methods will allow you to expand your “universe” of cases that will provide authority for your legal arguments. 

  • You can look “behind” by reading your case and noting what authority it relied upon.  

  • You can look “around” by using headnotes and topic areas for related cases. 

  • You can look “ahead” by seeing how more recent cases have treated yours, both positively and negatively. Ultimately, you’ll have to determine if your case is still “good law by using citators (like Shepard’s and KeyCite). 


The headnotes assigned by Lexis and Westlaw attorney-editors are useful in identifying key points of law in the case and finding similar cases.

Tips for using headnotes: 

  • Find the headnote or headnotes that focus on your area(s) of research interest

  • Use them to “jump” the part of the case where the judge discusses your area(s) (remember: you can’t cite a headnote!)

  • Read! What cases and other authority is the judge citing? Are they helpful? Add them to your “universe”


Use headnotes to find more recent cases that cite your case on your point of law. 

  • ​​​​​​​Using the headnote eliminates the possibility your case is cited on another issue, such as a procedural matter.
  • Look for “Cases that cite this headnote” in Westlaw


Example: Using Headnotes in Westlaw to find cases that cite to your case


Shepardize® - Narrow by this Headnote in Lexis+


Example: Using Lexis+ to narrow by headnote



  • Remember, with this method your original “good case” will be cited. That means these new cases will be more recent, may expand or narrow the original ruling, and most likely the largest number of cases will be from the same jurisdiction as the original case.


The video below walks through using headnotes to locate additional cases. 


You can also use a case citation to locate secondary sources that will help you understand the area of law and identify additional cases. 

Topic & KeyNumbers

Use KeyNumbers (on Westlaw) or Lexis’s topic system to find related cases even if they don’t cite your original case.

Using KeyNumbers in Westlaw:

  • Select “grid view” in Westlaw to see the Key Numbers
  • Select a narrow Key Number.

Example: Using Westlaw KeyNumbers to find related cases


  • You may want to change your jurisdiction at this point if your original case was good, but outside your jurisdiction (e.g. you found a good explanatory case in a secondary source, but it was from the “wrong” circuit)


Example: How to change jurisdiction when using Westlaw KeyNumbers

Using Topics in Lexis:

  • According to Lexis, “More Like This Headnote” uses “a Lexis search algorithm ... enhanced to bring in equivalents to some legal terms and phrases.” You may have a large number of results, so narrowing using filters and keywords may be very useful here.
  • Just above the headnote in Lexis, you will find Lexis topics (not to the right as they are in Westlaw). Pull down the menu and select “documents.” These results are the result of Lexis editors placing items in categories rather than using an algorithm. You may also need to using filters and keywords to narrow these results.


Example: Using Topics in Lexis


Citators can help you determine whether the case you've pulled is still "good law."

  • In a general sense, a citatory is a tool that connects you to anything that cites your case, statute, etc. This is often a lot of material including secondary sources. 

  • Whether you realized it or not, when you were using “Cases that cite this headnote” in Westlaw Precision or Shepardize® - Narrow by this Headnote in Lexis+, you were using Citators. In Westlaw, the citator system is called KeyCite and in Lexis, it is called Shepard’s. 

  • However, one very important way to use these citators is to determine if a case can be cited in your jurisdiction as authority. In other words, is it still good law. 

  • When we do this, we focus on more recent cases, statutes, or regulations that have had a negative effect on the authority of our case. 

  • This can be tricky because a point of law in our case may be “abrogated” by a case that doesn’t even mention our case! 

This video covers the basics of using citators on Lexis and Westlaw.