This article looks at numeral incorporation in Russian Sign Language (RSL). Numeral incorporation is the simultaneous combination of a numeral and a base sign into one sign. Incorporating forms typically use the numerical handshape combined simultaneously with the movement, location, and orientation of the base lexical sign; for example, "three months" will be expressed through an incorporating form 3_month. RSL is a language with a two-handed numeral system. Investigating two-handed numeral incorporation in RSL provides important insights into the constraints on numeral incorporation across languages as well as into the phonological structure of RSL.

Numeral incorporation is a general preference in RSL that is highly constrained: not all calendric terms can incorporate, and not all numbers can be incorporated. For example, the sign month incorporates numbers one through nine (one through five are one-handed, and six through nine are two-handed). The incorporating one-handed form 5_minute exists, while the two-handed *6_minute form does not occur (that is, its meaning is expressed sequentially), and the sign day does not incorporate numbers at all. These limits are conditioned for semantic (lexical frequency, pragmatics) and phonological reasons. Because the numeral system of RSL is two-handed, the results show, first, that numeral incorporation is not limited to one-handed numerals. In addition, the results indicate that limits on numeral incorporation are not universal across sign languages. In RSL, each paradigm shows specific numeral incorporation limits that are phonologically conditioned. These limits are explained by the interaction of phonological rules at all levels of sign sublexical features for both the numeral and lexical sign: location, orientation, handshape, and movement.

The location and orientation parameters of sign, however, have not been previously noted as being factors that limit numeral incorporation and sign complexity in a sign language. Our analyses, from both the numeral incorporation data and from elicitation and RSL corpus data, show that location and orientation function as phonological constraints in the composition of two-handed signs. Specifically, location and orientation operate in handshape symmetry restrictions. Our analyses also show that signs located on the head do not allow two-handed numeral incorporation. The corpus analyses corroborated this finding: all two-handed signs on the head that we found in our RSL corpus were symmetrical and frequently included weak drop, such that we found no asymmetrical two-handed signs on the head. Another symmetry restriction relates to orientation. Analyses of the RSL numeral incorporation data and the RSL corpus data and dictionaries show that RSL disprefers asymmetrical handshapes in two-handed signs having lateral orientation (palm facing the central line) (Fenlon et al. 2013).