Desiderative たい-Form (Pre-ます-Form VERB + たい as “want to VERB”)
In the Japanese language, when one says that they want something, as in a particular object, the Xがほしい grammar pattern is used and the phrasing がほしい is simply placed after the NOUN object, X, that is desired. However, when one says that they want to do something, as in perform a particular VERB action, a separate grammar pattern is used. This grammar pattern is using the Desiderative たい-Form of the VERB, which is represented by the construction Pre-ます-Form VERB + たい, which translates to “to want to VERB.”
Despite this grammar pattern being a VERB conjugation of sorts, the compound word that is the Pre-ます-Form of a VERB with the phrasing たい attached at the end is for the most part considered an い-Adjective word. For this reason, the word です can be seen succeeding the Desiderative たい-Form in formal sentences; there are many other grammatical instances where its status as an い-Adjective can be seen (such as the usage of the particle が as a direct object marker). Additionally, in the same way that the Xがほしい grammar pattern has the separate ほしがっている construction when used to refer someone else’s desires in the third-person, the Desiderative たい-Form has the alternative Pre-ます-Form VERB + たがっている construction. When this grammar pattern is used in the first-person, both particles が and を can be used as direct object markers, with the former placing a slight emphasis on the direct object being the object that is wanted to be VERBed. However, when this grammar pattern is used in the third-person with the たがっている construction, を must be used and cannot be replaced by が as the direct object marker.
suru (する) [to do] = shitai (したい) [to want to do]
taberu (たべる) [to eat] = tabetai (たべたい) [to want to eat]
nomu (のむ) [to drink] = nomitai (のみたい) [to want to drink]
asobu (あそぶ) [to play] = asobitai (あそびたい) [to want to play]
katsu (かつ) [to win] = kachitai (かちたい) [to want to win]
Kuruma ga kaitai na.
(“I want to buy a car.”)
Kare no kao wo mitakunai.
(“I don’t want to see his face.”)
Kanojo wa Disneyland (h)e ikitagatteiru.
(“My girlfriend wants to go to Disneyland.”)