Common Words:
* if
* in
* on
* up
* go
* so
* as
* is
* it
* at
* of
* to
* no
* do
* by
* be
Less Common Words:
* am
* an
* ax
* he
* me
* my
* we
* or
* oh
* ox
* pi
* us
Note: This list includes words that are commonly used in English. There are other two-letter words, but they might be considered archaic, abbreviations, or specific to particular contexts.