Why did the Elric brothers only believe in one rule of alchemy?


In the opening of Fullmetal Alchemist, it says...

> Human kind cannot obtain anything without first giving something in return
> To obtain, something of equal value must be lost That is alchemy's first law
> of equivalent exchange. In those days, we really believed that to be that
> world's one and only truth.

But why did the Elric brothers believe this to be the one and only law of
alchemy? If this was explained in one of the episodes of Fullmetal Alchemist
or Brotherhood, please list it too, thanks.




Okay, so, there's a couple things in play here you need to be aware of. Keep
in mind that some of this is slightly speculative.

First, it is _only in the dub_ that Alphonse states it to be the "one and
only" truth. The original commentary states,

> その頃【ころ】、ぼくらは、それが世界【せかい】の真実【しんじつ】だと信じて【しんじて】いた。
>
> "When we were young, we believed that to be the truth of the world."

Second, though, I think there is an important reason that Alphonse brings this
up. Starting at episode 43, the pre-OP commentary changes to the following:

> He who obtains [the Philosopher's Stone] is exempt from the rule of
> Equivalent Exchange and does not have to sacrifice anything to obtain
> something.

_(Note: This statement is somewhat wrong: During this unusual exchange, there
is still something lost, but it's not apparent to whomever it is doing the
transmutation.)_

In their adventure, Ed and Al basically learned that human lives are given an
alchemical value; since they both believe human life to be invaluable, this
shakes the foundation of the principle of Equivalent Exchange that they grew
up learning.

This seems to be the only reason that Alphonse used the past tense with
"believed"; the Philosopher's Stone shattered what they believed Equivalent
Exchange truly meant. To him, Equivalent Exchange can no longer be the "one
and only" truth.

This idea also holds true in _Brotherhood_. The Philosopher's Stone is
essentially identical, and the brothers learn the same terrible details of it.




Okay, so, there's a couple things in play here you need to be aware of. Keep
in mind that some of this is slightly speculative.

First, it is _only in the dub_ that Alphonse states it to be the "one and
only" truth. The original commentary states,

> その頃【ころ】、ぼくらは、それが世界【せかい】の真実【しんじつ】だと信じて【しんじて】いた。
>
> "When we were young, we believed that to be the truth of the world."

Second, though, I think there is an important reason that Alphonse brings this
up. Starting at episode 43, the pre-OP commentary changes to the following:

> He who obtains [the Philosopher's Stone] is exempt from the rule of
> Equivalent Exchange and does not have to sacrifice anything to obtain
> something.

_(Note: This statement is somewhat wrong: During this unusual exchange, there
is still something lost, but it's not apparent to whomever it is doing the
transmutation.)_

In their adventure, Ed and Al basically learned that human lives are given an
alchemical value; since they both believe human life to be invaluable, this
shakes the foundation of the principle of Equivalent Exchange that they grew
up learning.

This seems to be the only reason that Alphonse used the past tense with
"believed"; the Philosopher's Stone shattered what they believed Equivalent
Exchange truly meant. To him, Equivalent Exchange can no longer be the "one
and only" truth.

This idea also holds true in _Brotherhood_. The Philosopher's Stone is
essentially identical, and the brothers learn the same terrible details of it.

