Signs or words in American Sign Language (ASL) can be categorized into three types: one-handed, two-handed symmetrical, and two-handed non-symmetrical.
One-handed signs are formed with only one hand; some one-handed signs are body-anchored. For example, orange below. The signer is dominantly right-handed. For right-handed signers, use the right hand as dominant or active. For left-handed signers, use the left hand.
More examples of the one-handed signs are: feel, police, doubt, sick-of, deaf, yellow, FLY.
Two-handed symmetrical signs use both hands in a symmetrical handshape and movement (including alternative movement). For example, WANT, MAYBE.
More examples: depressed, contact, signing, race, game, book.
Two-handed, non-symmetrical signs have one dominant hand which moves and one passive hand which serves as a base. For right-handed signers, the right hand is the active or dominant hand, while the left hand is the passive or base hand. For left-handed signers, it is the opposite.
More examples: read, help, investigate, painting.
Now here comes a very interesting discovery as to why some signs have certain rules of movement and handshape.
Linguist Robbin Battison (1978) proposed two conditions: Symmetry Condition and Dominance Condition on two-handed signs. He identified these two structure constraints which explain the following "what-if" conditions.
The Symmetry Condition states that, if both hands of a sign move -- either alternating or simultaneous, then the handshape, the movement, and the location must be the same.
E.g. bath, maybe, party, play, earthquake, ball, story, etc.
The Dominance Condition states that, if the hands of a two-handed sign don't have the same handshape, then the dominant or active hand can move only while the passive hand stays in one place. That is, the passive hand acts as a base.
What's more, the passive hand in the Dominance Condition is restricted to one of a small set of the handshapes: A, S, B, 5, G (1), C, and O. These handshapes are called unmarked handshapes.
Examples: enough, cookie, helicopter, popular, pay-off, octopus, etc. The passive hand of these signs has only one of these unmarked handshapes.
Interesting, these unmarked handshapes are also the first handshapes that a child acquires ASL during the first three years from birth. These are evidences of a natural rule that governs the structure of signed words and the brain. Native signers didn't consciously create this rule.
But, but, there are some ASL signs that have the same handshapes, but the dominant hand moves while the base hand is stationary, such as work, easy, school. Why? Here comes another level of the rule explained by Battison.
If both whole hands with the same handshape are in contact, a passive hand is stationary while the dominant whole hand moves. E.g. school, paper, right, institution, work, proof/prove, how, easy.
If both hands with the same handshape are in contact and the fingers only move, both hands move. E.g. rabbit, starbucks, contact, Austria.
If you are a right-handed signer, your right hand is the active/dominant. If you are left-handed, your left hand is the active-dominant. Do not switch the active and passive roles of the hands. Stay consistent (even if you are ambidextrous).
Battison, Robbin. 1978. "Lexical borrowing in American Sign Language." Silver Spring, MD: Linstok.
Robbin Battison. "Analyzing Signs". Linguistics of ASL. Pp 193-212.
Clayton Valli, et al. "Linguistics of American Sign Language: An Introduction." Washington, D.C.: Gallaudet University Press. 2005. Pp 17.
Charlotte Haker-Shenk and Dennis Cokely. "American Sign Language: A Teacher's Resource Text on Grammar and Culture." Washington, D.C.: Gallaudet Press. 1980.
Which right-handed or left-handed should you sign?