преподавать - help!
How come the verb преподавать is conjugated in the present without the ва, as is usually the case? Rather than преподаваю, it's преподаю. Why is this verb different? Is it in a certain category of verbs different from the other -авать's?
No, in fact that's how verbs with the ending "-авать" conjugate normally.
Вставать - встаю ("to get up")
Давать - даю ("to give")
Узнавать - узнаю ("to learn [a new fact]")
Уставать - устаю ("to get tired")
Создавать - создаю ("to create")
Продавать - продаю ("to sell")
Verbs where the "-ва-" doesn't vanish when they are conjugated are different. In those cases "-ва-" is a suffix instead of a part of the ending, and the ending is just "-ть". That's why the "-ва-" is present in all forms.
Verbs that end in -овать, normally behave this way. For example, рисовать, анализировать lose their ова and add у instead (more precisely, у + й, i.e. the ending vowel will always be iotated): рисую, анализирую.
Sometimes it also works for -евать verbs. Танцевать belongs to that class. However, недоумевать ослабевать do not. I read that a lot of verbs based on loanwords work that way, and also verbs based on nouns, so, for танцевать it is a fairly good match (it originates as German Tanz ).
What Kundoo said is mostly but not quite correct. Russian verbs ending in -авать have one of the five stems: -ставать, -знавать, -давать, -создавать — or плавать. Плавать is regular (плавать→плаваю), the rest lose their -ва in their non-past conjugation.
Same with -ывать, which is a popular secondary imperfectivisation suffix. The conjugation pattern is the same as that of читать.
- I think it might change in the future for some imperfectivisations of biaspectual verbs. Verbs like организовать can be used in either of two aspects but some do have an imperfectivised version (организовывать). If native speakers use организовывать as the infinitive but the forms of организовать as its conjugated forms, it may eventually lead to the latter forms merging into the paradigm of the former.