Discussion Groups / English Usage / February 2010

There are two uses of "train". One is transitive the other is
intransitive.

OED:

   6. To subject to discipline and instruction for the purpose of
      forming the character and developing the powers of, or of making
      proficient in some occupation. (Also with up.)
   a. To instruct and discipline generally; to educate, rear, bring up.
b. To instruct and discipline in or for some particular art,
      profession, occupation, or practice; to exercise, practise,
      drill; to make proficient by such instruction and practice (see
      also TRAINED ppl. a.). Const. in, for, to.
   
   7.
   a. intr. for pass. To undergo or follow a course of instruction
      and discipline; in early quots., to go through a course of
      military drill, to drill.
   b. intr. With adv. To get into some condition by training;

"I am trained in [the subject]" - "I was taught and am proficient in
[the subject]".

"I trained in [the subject]" - "I learned and am proficient in [the
subject]".

Good.  One more thing, though ...

 > Why do not I need the auxiliary verb "be"

While it's true that "do not" is what "don't" unpacks into,
it's nevertheless also true that "don't" is a single verb
which moves to the front of a question, while "do not"
is not a single verb, so that only the "do" should move.

The "not", if it's not contracted with "do", has to stay
with the rest of the verb phrase on the other side of
the subject when "do" is moved around it to the front:

    I [don't] need it.  ~  I [do not] need it.

    [Don't] I need it?   ~  [Do] I [not] need it?
   *[Do not] I need it?

    Why [don't] I need it?  ~  Why [do] I [not] need it?
   *Why [do not] I need it?

-John Lawler                   http://www.umich.edu/~jlawler
Getting an education is a bit like a communicable sexual
 disease.  It makes you unsuitable for a lot of jobs, and
 then you have the urge to pass it on. -- Terry Pratchett