Definition
In civil law, solidum refers to a whole, entire, or undivided thing — most commonly encountered in legal usage through the phrase in solidum, meaning liability for the whole of an obligation rather than a proportionate share. A party bound in solidum is liable for the entire debt or obligation, not merely a fractional part, and creditors may pursue that party for the full amount regardless of whether others share the same obligation.
The term itself is the foundation for several related civil law doctrines and phrases, particularly those governing joint and several liability in civilian jurisdictions.
Common Language
Modern common usage (Wiktionary): The die or base component of a pedestal; alternatively, a complete sum.
Historical common usage: Not separately defined in Webster's 1913 as a standalone entry; the root concept of "solid" carried meanings of wholeness, firmness, and undivided completeness.
Editorial note: The architectural and mathematical senses of solidum in common usage capture the core idea of wholeness, but neither conveys the liability dimension that dominates legal usage. A researcher encountering the term outside a legal text would not intuit its application to joint and several obligations.
Common Confusion
Solidum is frequently encountered only as part of the phrase in solidum and may be misread as merely a synonym for "jointly" in the sense of shared liability. The critical distinction is the opposite: in solidum means each obligor is liable for the entire amount, while liability pro rata parte means each is liable only for their proportionate share. Conflating these two Latin phrases produces a fundamental misreading of the obligation's structure. See IN SOLIDUM and PRO RATA.
Recognized Forms
/SUBTYPES
Solidum as a standalone term is the parent concept underlying several recognized phrases:
IN SOLIDUM — The operative form in most legal texts. Liability for the whole. A creditor may demand full performance from any one of multiple obligors bound in solidum.
SOLIDUS LEGALIS — A distinct monetary term derived from the same root. In English legal history, the solidus legalis was a coin or money of account equal to 13 shillings and 4 pence. Originally a gold coin of the Byzantine Empire, the term was applied to various coins and monetary units in medieval usage and is considered a linguistic ancestor of the modern "shilling."
Why It Matters in Research
Solidum rarely appears alone in legal sources — researchers will encounter it primarily embedded in phrases, particularly in solidum, and must recognize it as the root concept anchoring civil law discussions of joint and several liability. This matters for several reasons:
First, civilian jurisdictions (Louisiana, Quebec, and mixed-law systems) use the in solidum framework where common law jurisdictions use joint and several liability. These are functionally similar but not identical, and sources using solidum terminology are almost certainly drawing on civilian rather than common law tradition. A researcher applying common law joint and several liability doctrine to civilian solidum sources risks importing inapplicable distinctions.
Second, the monetary usage — solidus legalis — appears in English legal history texts with no connection to the liability doctrine. Historical sources such as Stephens' Commentaries use the term in a purely numismatic context. A researcher working across both bodies of source material must distinguish which sense of solidum is operative.
Third, Anderson's Dictionary of Law cross-references CONSOLIDATE and IN SOLIDUM without defining solidum independently, a pattern that signals the term's dependence on its phrasal context. Burrill similarly routes the reader to in solidum. This means that searching for solidum alone in older indices or digests will often yield incomplete results; effective research requires searching the full phrase.
Fourth, the maxim solo cedit, quicquid solo plantatur (what is planted in the soil belongs to the soil) appears in Rapalje & Lawrence immediately adjacent to the solidum entries. This juxtaposition in older dictionaries reflects alphabetical proximity, not conceptual connection — researchers should not infer a doctrinal link between solidum liability concepts and accession doctrine.
Historical Dictionary Support
The historical dictionaries converge on the core definition without meaningful divergence: solidum is a whole or undivided thing. Black's (both editions), Rapalje & Lawrence, and Burrill are in agreement on this point, and each routes the reader to in solidum for the operative legal doctrine.
Black's second edition adds the most substantive historical content, noting the Byzantine origins of the solidus coin, its evolution through medieval monetary systems, and its proposed etymological connection to the English shilling. This numismatic history, drawn from Stephens' Commentaries, is reliable but limited in scope and does not bear on the liability doctrine.
Rapalje & Lawrence provides the most practically useful framing for legal researchers, explicitly contrasting bound in solido (liable for the whole) with bound pro rata parte (liable for one's share only). This contrast is the functional core of what solidum means in legal practice, and it is the most instructive summary across the five sources.
Anderson's entry is a bare cross-reference, which itself signals that the term was considered well-understood by derivation from its related phrases rather than requiring independent treatment.
Jurisdictional Note
Solidum and in solidum terminology appear most frequently in Louisiana law, Quebec civil law, and scholarly treatments of Roman and civilian legal systems. Common law jurisdictions use joint and several liability language instead. Researchers working in Louisiana legal materials will encounter in solidum as live doctrine; researchers working in other U.S. jurisdictions will encounter it primarily in historical or comparative contexts.