About Japanese Plain-Form Verbs and Politeness

One thing that had me stumped for a while was the complex relationship of Japanese verbs and politeness levels.  Most Japanese educational materials start you off learning the "~masu" form, also called the "polite form."  It's very helpful, so you don't accidentally offend someone, but can come across as somewhat reserved if used frequently.  All of this came crashing down around me when my class started plain form verbs.  When do we use them?  Why?  And how the heck does conjugation work?  Let's find out and learn some plain-form verbs!
To start, I suppose we can say there are about 5 levels of politeness in Japanese:
  • Level 5 – Honorific/Humble: certain words are substituted to increase the politeness level when speaking of or to a superior (honorific), or of your own actions (humble).  The passive voice can be used as honorific, but is less respectful that an honorific/humble conjugation or the replaced-word.  All honorific verbs have a dictionary form (plain form) base, which is used in clauses. (He said he would eat it. itadaku to iimashita) To eat: meshi-wo-agarimasu (honorific) / itadakimasu (humble).
  • Level 4 – Without using Level 5, we can still achieve a higher level of politeness by changing the verbs into their “~masu” form.  This shows respect toward your audience, but not necessarily your subject.  Good for general conversation, especially when mixed with level3. To eat: tabemasu
  • Level 3 – By using “'ndesu” at the end of a Level 2 verb, we can bump up the politeness of a sentence without sounding too formal or too informal.  For negative conjugations (etc.) the "ndesu" can be shortened to just "desu," especially as "ndesu" has an explanatory nuance.  I would use "-masu" for plain present and a conjugation with "desu" for other forms with other "-masu" conjugations ("-masen," etc.) interspersed.  It can sound nosy if used too much. To eat: taberu'ndesu
  • Level 2 – An intimate form used between close friends and family as well as in the smaller phrases that occur in complex sentences, such as “the boy wearing a blue coat.”  Plain form can be used by superiors to speak to their inferiors, but vis-versa cannot be applied. To eat: taberu
  • Level 1 – Vulgar or colloquial language; the word choice maybe deliberately course, a matter of sex/gender or dialect To eat: kuu.
So, how do we use this?  In my opinion, learning "-masu" first is double-edged; you can speak to most anyone without sounding arrogant, but it sounds aloof... and it makes conjugation harder.  Take "ikimasu," which can come from iku (to go) or ikiru (to live).  If I am learning hiragana and I have to conjugate these words, with out context, which is right?  Sadly, I cannot tell you, but as your studies continue, you will have to learn both "-masu" and its correct plain-form as you go.
Aside from the levels of politeness, as noted above there are several types of dictionary/plain form verbs:
• The regular -eru and iru (ichidan verbs)
• Then the semi-irregular groups of: -su; -ku; -gu; -tsu; -ru; -u; -nu; -mu; -bu, some with additional irregular verbs, usually in the -te and -ta forms
. • And the completely irregular suru and kuru
Plain Positive: These are also called the “dictionary form” because we find verbs in this form while consulting a dictionary. Every verb, including honorific and vulgar words has a plain form. In their plain form, these verbs have their own distinct way of behaving. In their natural form, these verbs are in their imperfect tense (to ~), but can mean “does,” “will do in the future,” or “will as a matter of habit.”
taberu - (to eat)
miru - (to see)
haku - (to wear pants/shoes)
nugu - (to undress)
kasu - (to lend)
matsu - (to wait)
toru - (totake)
  *beware: some verbs that end with iru/eru but are this type of verb
kau - (to buy)
shinu - (to die)
yomu - (to read)
tobu - (to fly)
suru - (to do)
kuru - (to come)
EX: John eats/will eat sushi. : Jon wa sushi wotaberu.
In the case of “desu,” we have two forms: da (used for casual speech and in newspapers and books) and de aru (for formal public addresses, such as speeches and official address) and expository writing.
Plain Negative: In this form, we create the opposite of the plain positive, and as one would think, these words be come “does not~,” “will not do in the future,” or “does not/will not do as a matter of habit.”  We can think of verbs in two ways: ichidan (one step) and godan (five step)
. iru/eru: These are the ichidan verbs: one step - remove final ru and add nai (nai).
taberu – tabe – tabenai - (to not eat)
miru – mi – minai - (to not see)
In the other verb's cases, let's make an easier way to conjugate for now and the future. These verbs, the godan verbs, can reflect the 5 vowel sounds: A I U E O. Let's order these as A = 1, I = 2, U = 3, E = 4 and O = 5. To create the negative, all we must do for these verbs is simply change the U-sound (3) into the corresponding A-sound (1) and add nai.
haku – haka – hakanai - (to not wear pants/shoes)
nugu – nuga – nuganai - (to not undress)
kasu – kasa – kasanai – (to not lend)
matsu – mata – matanai - (to not wait)
toru – tora – toranai -  (to not take)
  *beware: some verbs that end with iru/eru conjugate like this type of verb
  *the verb aru is irregular in this case: aru – nai to not exist (inanimate)
kau – kawa – kawanai - (to not buy)
  *this form is irregular through out -u verbs when concerning any 1 stem
. shinu – shina – shinanai – (to not die)
yomu – yoma – yomanai – (to not read)
tobu – toba – tobanai – (to not fly)
The irregular verbs, being irregular, need to be memorized for their correct conjugation:
suru becomes shinai – (to not do)
kuru becomes konai - (to not come)
 EX: John doesn't eat/will not eat sushi. : Jon wa sushi wo tabenai.
Desu, becomes janai in casual communication or dewa nai for expository documents and public speeches.
Plain Past-Tense: One of the more vexing plain verb forms comes from a contraction of 2 (I) with ta; long ago the plain form was made with the "-masu" stem, but has since changed to this current system, although some verbs preserve this antiquated mode. Pay close attention to the divisions made because the grouped verbs behave the same:
iru/eru: Remove final ru and add ta
taberu - tabe - tabeta (ate)
miru - mi - mita (saw)
ku/gu: Change ku/guinto ita/ida. The ten-ten remains preserved; i.e.: GU - IDA
haku - ha - haita (wore pants/shoes)
nugu - nu - nuida (undressed)
su: Changes into shita
kasu - ka - kashita (lent)
tsu/ru/u: Becomes tta matsu - ma - matta (waited)
toru - to - totta (took)
  *beware: some iru/eru verbs conjugate this way
kau - ka - ka?ta (bought)
nu/mu/bu: Becomes nda
shinu - shi - shinda (died)
yomu - yo - yonda (read)
tobu - to - tonda (flown)
Irregular: Must be memorized
suru - shita (did)
kuru - kita (came)  iku - itta (went)
Past Negative   Coincidentally, to achieve the PAST-NEGATIVE, all we have to do is conjugate the final -nai of any negative-tense as we would a negative adjective.  We drop the final i and add katta.  All verbs follow this pattern.
taberu – tabenai – tabenakatta (did not eat)
Desu and da become datta in informal exchanges . de atta can be used in the case of official notices or speeches.
V²’te-Form: The so called -te form is handy. By knowing it, we can begin to stack sentences to create longer and more complex thoughts, such as creating a sequence of actions, listing items or qualities and expressing modes of how something is done among other complex ideas.  It follow the same patterns as the plain-past, but ends with -te or -de, obviously.  It has not inherent past or present connotation, and actually it has no direct translation into English, although a -te form utterance is usually a request.
iru/eru: Remove final ru and add te
taberu - tabe- tabete (to eat)
miru - mi - mite (to see)
ku/gu: Change ku/guinto ite/ide. The ten-ten remains preserved; i.e.: GU - IDE
haku - ha - haite (to put on pants/shoes)
nugu - nu - nuide (to undress)
su: Changes into shite
kasu - ka - kashite (to lend)
tsu/ru/u: Becomes tte
matsu - ma - matte (to wait)
toru - to - totte (to take)
  *beware: some iru/eru verbs conjugate this way
kau - ka - katte (to buy)
nu/mu/bu: Becomes nde
shinu - shi - shinde (to die)
yomu - yo - yonde (to read
) tobu - to - tonde (to fly)
Irregular: Must be memorized
suru - shite (to do)
kuru - klte (to come)
iku -itte (to go)
For negative forms, the i is removed and is replaced by kute.  This is used in some grammatical patterns and is used as a conjunctive.
tabenai - tabena - tabenakute
Desu becomes de.
I hope this has been informative and helpful and not too garble; there' a lot of info in there!  I would like to close by saying that by the end of the first year of Japanese study, you should have these forms as well as the -masu forms well in hand.  That said, good luck!  Ganbatte~
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