Personally, just because you can get away with something isn’t a reason to do it, for me… but that’s just me. And I think a textbook shouldn’t be taking that route, that just because you can get away with it, it’s okay.
Add to that the previously mentioned aspects that make the plain forms more irregular and you have the arguments for those who want teaching materials to start with polite.
the way I see it it’s less about “getting away with it” but more staying in your lane and learning things in a step by step, logical manner. Your speech won’t be situationally appropriate no matter how hard you try to at first anyways so I think focussing on the most fundamental aspects of the language goes before trying extra hard to be culturally sensitive. That’s also just me though.
No problem. 
This was just a quick look through. I’m sure ている is there somewhere. As for casual volitional, it’s possible it’s in book 4 or something.
This is mostly why I stopped using the book series. It served me well for the first two books, but by book three I’d absorbed so much from looking random things up that I heard watching anime that I already know most of the content. This is also why I didn’t bother getting book four.
I’ve discussed it with my girlfriend and she has said what many people on the “plain first” side have said, that she wouldn’t be offended by a foreigner using plain language with her. Though, she also made the caveat that as a Kansai-jin she also wouldn’t be offended by a native Japanese using plain language either, on the street for instance, like a foreigner traveler would be in the situation to. I’m not sure all Japanese would feel the same way, but that’s just for context.
However, she also agreed that using polite language in such a situation would really only leave a positive impression. Japanese people learn the polite expressions after the plain, so they often make the mistaken assumption that foreigners do too, so they might interpret the use of polite language as an intentional effort at politeness rather than the only means of communication it might often be. I mean, unless the person was really in over their head trying to use all kinds of nonsense keigo they didn’t understand.
So you’re left with the option to frame things as “really no impression either way” or “potentially positive impressions” and that’s the route that I think is most appropriate for teaching materials to go for.
Maybe I’m too far into “the curse of knowledge” territory to have strong feelings about whatever potential damage people might incur from not taking the absolutely most “logical” route in learning verb conjugations. Thinking about formulas for how to conjugate verbs is not something that I do much.
That might also explain, or contribute to, Japanese people assuming I know way more than I do after saying a few sentences. [I quickly disappoint them 
]
I didn’t even know starting with polite forms was a thing, I thought learning dictionary form first was the only way that made sense, because of conjugations and all that.
Of course I’m absolutely biased towards dictionary form first, but doing it the other way just seems backwards and confusing to me.
Interestingly, I learned ます first, and I wouldn’t want it any other way.
I guess the way we learned does affect the way we think about the situation.
Edit: @jprspereira I learned with みんなの日本語
You can find the list of grammar points here
It teaches the てform from Chapter 14 to 16, 2 or 3 different cases at the time (starts with ichidan and る/つ/う verbs, then some other combos, then the remainder).
The plain form is part of chapter 20, but it was already discussed a little bit earlier at the time of the てform
It’s much easier to just make a chart that says はは = your own mother and おかあさん = someone else’s mother,
This is exactly how they taught us in high school actually. はは = your mum; おかあさん = someone else’s mum, and we never spoke of it again. I only found out about the other hierarchical aspects from self study/reading forums/whatever native Japanese content I was consuming at the time.
Maybe I’m too far into “the curse of knowledge” territory to have strong feelings about whatever potential damage people might incur from not taking the absolutely most “logical” route in learning verb conjugations. Thinking about formulas for how to conjugate verbs is not something that I do much.
This, too. Even though I learned polite first, plain/plain past/て form is mostly automatic at this point. It’s the passive/potential/causative that can be annoying sometimes but I think that’s more related to the difficulty of the conjugation/the situation in which you’d use those as opposed to some kind of ‘curse of polite first’ thing.
Here’s my 2c - I started learning Japanese at high school. We started with です/ます form, and I think that was the right call for us.
For て form, we just learnt to conjugate from the stem form. Our teacher taught us a classic song (I’m presuming others learnt the same song).
い・ち・り→って
み・び・に→んで
き・ぎ→いて・いで
し→して
From memory, we learnt every conjugation from the stem form of the verb until we we introduced to plain form.
We exclusively learnt ます・です form for quite a while actually, before being introduced to plain form. I guess we were 13, so maybe if I was starting now (at 23), I could have handled more faster 
I don’t have any difficulty switching between them now, but I’m glad I started with ます because I’d rather default to the polite end of the scale.
I think this is a good example of why this stuff is important to study. The above is an oversimplification. “addressee honorifics” are the です ます でございます forms. They show politeness to the person you are adressing.
“referent humble and honorific forms” raise or lower the status of the thing that you are talking about. There are the お ご nouns and the verbs like 申す and the honorific verb forms.
These two axises of politeness can exist independently of each other. You can speak です・ます form without using humble or honorific language (this is extremely common, you are being polite to the person you are addressing while being “neutral” toward the thing you are talking about). Also (maybe less common) you can speak in a plain style while still using referent honorifics (if you were talking to a classmate about what the teacher did, you could be speaking in plain style but still use an honorific verb form to describe the action).
ます and です, お and ご are 丁寧語.
丁寧語 is usually referred to as polite language.
尊敬語, which is what jpr was talking about, is usually called honorific or respectful language.
I don’t really see how what he said could be considered wrong.
お and ご also appear in other subcategories, but he wasn’t getting into that.
Honorific language doesn’t nessesarily “increase the status of the person you are adressing”. If me and you are working at a company and i refer to a customer as お客様, I am not elevating your status by using that language.
Okay, that part was an oversimplification, but that’s all, he is not making an exhaustive lecture on keigo. He said general, which implies there is more detail he knows he’s leaving out.
“oversimplification” is a better way to put it. I will edit
I learnt the “masu” form in lessons using Japanese for Busy People and knew of little else. After an hour or so at my girlfriend’s house (about a year after being in Japan) she said to me in English “my mum just asked why you are being so formal”. She’d already explained I knew nothing else. I’ve since taught some basic Japanese at a school club and I always start with stem and explain that the ending can be changed depending on tense, circumstance etc. I think this helps pupils to understand how simple/regular it is. I personally think books and courses should take a mixed approach such as this. It would help students to see the formation of the verb with stem and at the same time offer a basic way of forming simple and polite sentences for a wide variety of uses - although not perhaps for my girlfriend’s mum.
CTRL + F“purpose”: 0 results found
isn’t that a big factor regarding that question? why and for what purpose one is learning japanese?
• want to have conversations with strangers as soon as possible? learn polite form first.
• main goal is first talking to friends and family? learn casual form first.
i guess except if you’re just being introduced to your partners family
• you only focus on reading and comprehension and won’t converse any time soon anyway? learn what feels best or both simultaneously
not sure that question warrants that much thought in any case, though.
Yup, oversimplification precisely because the point was to introduce the general concept of politeness to beginners, not teach 
As a beginner, I felt like never learning this because there was no simple definition I could grab myself to, so everything seemed overwhelming. My point was to give the idea of “yooo, this exist… here’s a quick definition… we will be focusing on this form for now and I’ll drop you bits from the others along the way”. Once we get to the おかあさん vs はは thing (ex), the learner will be able to connect the dots.
Mind you, the point here was checking if there was a way to talk about honorific and humble without scaring the learner Plus, let’s be honest… a common reaction for people being introduced to the Japanese culture is “OHHHH THEY’RE SOOO POLITEEEEEE”. A brief explanation with some storytelling would be appreciated imo xD
I don’t think it matters at all.
Why? (genuinely curious)
(I realize this was posted days ago. I’m just now reading this thread)
Because that would be a lot of information all at once. Basically I was saying, one or the other needs to be first.