I know he explained it but I still don't get it.

It's messing me up when it comes to 天. He says when it's a primitive then the first stroke is right to left but as you can see I don't really understand what a primitive is (I understand radicals)
example
蚕 vs 添
or
奏 vs 笑

I don't have my book with my at the moment, but I'm pretty sure nest0r is right. Radicals are what the Japanese actually categorize kanji by, and are part of their teaching process. Primitives are an artificial thing Heisig made up that occasionally but not consistently matches up with the accepted radicals (try look up a kanji by radical. You'll quickly find a lot of your primitives don't exist, or at least not in that form). While Heisig's primitives do occasionally coincide with actual radicals, it's only out of convenient happenstance; he doesn't teach radicals, as a general thing.

I think the primitive/radical distinction you made for the top stroke of 天 was self-fabricated.. I don't believe he ever mentions radicals outside the introduction. I don't remember if he did have any guides on it, but I personally just remember it on a case by case basis. If you need to, just incorporate the differences into your mnemonic. Turn a slanted heaven into a fall from heaven or something (whee, slide!)

[Katsuo]

nest0r Wrote:I thought a 'primitive' was just a broader, Heisig-coined version of 'radicals', but I'm just guessing.

That's exactly right.

The 214 radical system was established about 400 years ago. (Wikipedia ref).

Heisig's system uses most of the radicals, and adds a couple of hundred more components and gives them all English names. (And calls them "primitives".)

I previously posted a radical / primitive equivalent list in another thread.

Regarding 天, the four-stroke component in numbers 634 添 "annexed", 938 笑 "laugh" and primitive 喬 "angel" is similar-looking but different. The KanjiGen classifies it as two separate components, katakana "no" & "large" (ノ & 大). (Not all sources agree, though.)

To avoid confusion, it would be better to think up a new primitive name for the above combination. And in fact Heisig does in RTK3, calling it "sapling".

Ok I get it now I guess, they're just more radicals combined, thanks. I had a hunch but some of the stuff he said was misleading me to believe that.

I misewell just call it early death from 夭 I suppose, since it seems to match it.

Yeah, the radicals classify the kanji. Etymologically, every part of a kanji can be traced back to the radicals. But a lot are very different now.