claims: Clarification/broadening of the independent claim: Independent claims are typically written with broad terms, to avoid permitting competitors to circumvent the claim by altering some aspect of the basic design. But when a broad wording is used, it may raise a question as to the scope of the term itself. If a dependent claim is specifically drawn to a narrower interpretation, then, at least in the U.S., the doctrine of claim differentiation states that the scope of the independent claim is strongly presumed be different from, and therefore broader than, the scope of the dependent claim. The doctrine dictates that it "is improper for courts to read into an independent claim a limitation explicitly set forth in another claim." This means that if an independent claim recites a chair with a plurality of legs, and a dependent claim depending from the independent recites a chair with four legs, the independent claim is not limited to what is recited in the dependent claim. The dependent claim protects chairs with four legs, and the independent claim protects chairs with four legs as well as chairs having two, three, five or more legs. Similarly, it may be unclear whether a "base" includes a "set of legs." A dependent claim, including the phrase, "wherein said base comprises a set of legs," if allowed by the patent examiner, clarifies that the word "base" in the independent claim does not necessarily include legs. In practice, dependent claims are often used to home in on the inventor's preferred embodiment of the invention (e.g., the actual product design that the inventor intends to use.) The independent claim broadly describes the invention; dependent claim #1 describes the invention in a narrower aspect that more specifically describes the preferred embodiment; dependent claim #2 is narrower still; etc. Possible invalidity of independent claim: It is impossible to know, when beginning the application process and even at the time of patent issuance, if a patent claim is valid. This is because any publication dated before the application's priority date and published anywhere in any language can invalidate the claim (excluding publications by the inventor published during the grace period in certain countries such as U.S., Canada and Japan). Furthermore, even applications that were not yet published at the time of filing, but have a priority date prior to the priority date of the application, can also invalidate the claim. As it is