Verbs that do not have tense or agreement endings are nonfinite (also called verbals).
Nonfinite verbs can be classified as consisting of five types: base forms, present participles, past participles, infinitives, and gerunds. (Some grammarians combine the categories of base form and infinitive.)
We watched the substance explode. [base form]
The growing yeast culture has special storage
requirements. [present participle]
The gas chromatograph fixed last week is
broken again. [past
participle]
When NASA first organized the Viking Lander missions to Mars, one of the
most vexing problems its scientists faced was devising and agreeing upon tests
to detect life. [infinitive]
--Kai Wu, "Artificial Life," SciTech Magazine
Nicolas Andry, the pioneer of orthopedics, had a special interest in
correcting deformities in
children. . . . [gerund]
--Linglei Xu, "Bone Talk," SciTech Magazine
