Japanese Plug and Play Ghetto Grammar (JPPGG©) #109
PLAIN FORM + KAMOSHIRENAI - to probably verb

In Japanese, to say that something will most likely happen in the future or to say that something has probably already occurred, we use the word ~kamoshirenai. Both Japanese nouns and Japanese verbs in plain form (i.e. Base III) can be used to which we can attach one of three variable endings which vary in politeness.
When used after nouns, or verbs in plain form, KAMOSHIREMASEN means: maybe noun, maybe verb, might have been noun, might have verb'ed, or probably noun, or probably verb etc. Although by definition, KAMO, by itself, is the word for duck, the origin or roots of the word KAMOSHIREMASEN come mainly from the verb to know, or, SHIRU. In this case, SHIRENAI means unable to know. The KA and the MO pose even more uncertainty when put together because KA is the question mark (?) particle, and MO is the also particle.
KAMO without SHIRENAI or SHIREMASEN is less polite but still understood. To use KAMO by itself is permissible when speaking with close friends or acquaintances. However, since saying just KAMO is less polite, beginners should avoid saying it. Its best to always use the most polite form KAMOSHIREMASEN, but it's ok to say KAMOSHIRENAI when you are in company of close friends etc.
If you were to listen to 10 minutes of any random Japanese conversation, you would most likely or probably (pun intended) hear the word KAMOSHIRENAI within that time. KAMOSHIRENAI is always used in Japanese conversation. Verbs in base III are equivalent to what is known as plain form, of the verb, sometimes designated in JPPGG© Ghetto Grammar as P.F.

Verb(Base III) + KAMOSHIRENAI - most common, but less polite

Verb(Base III) + KAMOSHIREMASEN - more polite

Verb(Base III) + KAMO - least polite and funny to the ear

1. TORARETA KAMOSHIREMASEN

It might have been stolen

2. SOTSUGYO^ SHISO?
SURU KAMOSHIRENAI

Are you going to graduate?
It's possible! (Maybe!)

3. ARE WA KAMO KAMO

Figure 1 A KAMO

It's a duck, probably.-or-
It's most likely a duck.-or-
It's probably a duck.-etc.

4. OISHII KAMO NE!

Its probably tastes pretty good! (Doesn't it?)
(Tasty duck hunh~)

As always, Ganbatte Ne!
Do your Best!
Makurasuki Sensei.