The transition phrase has a substantial effect on the scope of a claim. The most common type is an open-ended transition phrase, which is most often used for claims that cover most mechanical, electrical or computer-related inventions.

Open-ended transition phrases are used in most chemical cases, as well. However, partially open-ended or closed transition phrases are used in some cases. An example of an open-ended transition phrase is “comprising.” An example of a partially open-ended phrase is “consisting essentially of.” An example of a closed transition phrase is “consisting of.”

“Comprising” means including the following elements but not excluding others. Other open-ended transition phrases are “including,” “having,” “containing” and even "wherein.”

“Consisting essentially of" excludes other elements from having any essential significance to the combination. The phrase "consisting essentially of” allows elements that do not materially affect the basic and novel characteristics of the claimed invention. In chemical claims, the transition phrase “consisting essentially of” allows for the presence of small amounts of components outside of the designated composition.

The closed-end transition phrases “consisting” or “consisting of” limit the claim to the recited elements – no more or no less – in mechanical claims. In method claims, the phrase “consisting of” covers processes having only the recited steps. In chemical claims, the phrase “consisting of” excludes more than traces of other ingredients.