In heraldry, cadency is any systematic way of distinguishing similar coats of arms belonging to members of the same family. Cadency is necessary in heraldic systems in which a given design may be owned by only one person (or, in some cases, one man) at once. Because heraldic designs may be inherited, the arms of members of a family will usually be similar to the arms used by its oldest surviving member (called the "plain coat"). They are formed by adding marks called brisures, similar to charges but smaller. Brisures are generally exempt from the law of tincture.

In heraldry's early period, uniqueness of arms was obtained by a wide variety of devices, including change of tincture and addition of an ordinary. See Armorial des Capétiens and Armorial of Plantagenet for an illustration of the variety.

Systematic cadency schemes were later developed in England and Scotland, but while in England they are voluntary (and not always observed), in Scotland they are enforced through the process of matriculation.

The English system of cadency involves the addition of these brisures to the plain coat:

• for the first son, a label of three points (a horizontal strip with three tags hanging down)—this label is removed on the death of the father, and the son inherits the plain coat;
• for the second son, a crescent (the points upward, as is conventional in heraldry);
• for the third son, a mullet (a five-pointed star);
• for the fourth son, a martlet (a kind of bird);
• for the fifth son, an annulet (a ring);
• for the sixth son, a fleur-de-lys;
• for the seventh son, a rose;
• for the eighth son, a cross moline;
• for the ninth son, a double quatrefoil.

Daughters have no special brisures, and use their father's arms on a lozenge. This is because English heraldry has no requirement that women's arms be unique.

In England, arms are generally the property of their owner from birth - subject to the use of the appropriate mark of cadency. In other words, it is not necessary to wait for the death of the previous generation before arms are inherited.

The eldest son of an eldest son uses a label of five points. Other grandchildren combine the brisure of their father with the relevant brisure of their own, which would in a short number of generations lead to confusion (because it allows an uncle and nephew to have the same cadency mark) and complexity (because of an accumulation of cadency marks to show, for example, the fifth son of a third son of a second son). However, in practice cadency marks are not much used in England and, even when they are, it is rare to see more than one or, at most, two of them on a coat of arms.

Although textbooks on heraldry (and articles like this one) always agree on the English system of cadency set out above, most heraldic examples (whether on old bookplates, church monuments, silver and the like) ignore cadency marks altogether. Oswald Barron, in an influential article on Heraldry in the 1911 edition of the Encyclopaedia Britannica, noted:

"Now and again we see a second son obeying the book-rules and putting a crescent in his shield or a third son displaying a molet, but long before our own times the practice was disregarded, and the most remote kinsman of a gentle house displayed the "whole coat" of the head of his family."^[1]

Nor have cadency marks usually been insisted upon by the College of Arms (the heraldic authority for England, Wales and formerly Ireland). For example, the College of Arms website (as of June 2006), far from insisting on any doctrine of "One man one coat" suggested by some academic writers, says:

… The arms of a man pass equally to all his legitimate children, irrespective of their order of birth.

Cadency marks may be used to identify the arms of brothers, in a system said to have been invented by John Writhe, Garter, in about 1500. Small symbols are painted on the shield, usually in a contrasting tincture at the top. …^[2]

It does not say that such marks must be used.

In correspondence published in the Heraldry Society’s newsletter, Garter King of Arms Peter Gwynn-Jones firmly rejected a suggestion that cadency marks should be strictly enforced. He said:

“I have never favoured the system of cadency unless there is a need to mark out distinct branches of a particular family. To use cadency marks for each and every generation is something of a nonsense as it results in a pile of indecipherable marks set one above the other. I therefore adhere to the view that they should be used sparingly”.^[3]

In a second letter published at the same time, he wrote:

“Unfortunately, compulsion is not the way ahead for twenty-first century heraldry. However, official recognition and certification of any Armorial Bearings can only be effected when the person in whose favour the Arms are being recognized or certified appears in the appropriate book of record at the College of Arms. I believe it right in England and Wales for a branch to use cadency marks sparingly and only if they wish to do so.”^[4]

The system is very different in Scotland, where every male user of a coat of arms must have a personal variation, appropriate to that person's position in their family, approved (or "matriculated") by the Lord Lyon (the heraldic authority for Scotland). This means that in Scotland no two men can ever simultaneously bear the same arms, even by accident, if they have submitted their position to the Scottish heraldic authorities (which, in practice, in Scotland as in England, not all do). To this extent, the law of arms is stricter in Scotland than in England.

Scotland, like England, uses the label of three points for the eldest son and a label of five points for the eldest son of the eldest son, and allows the label to be removed as the bearer of the plain coat dies and the eldest son succeeds. In Scotland (unlike England) the label may be borne by the next male heir to the plain coat even if this is not the son of the bearer of the plain coat (for example, if it is his nephew).

For cadets other than immediate heirs, Scottish cadency uses a complex and versatile system, applying different kinds of changes in each generation. First, a bordure is added in a different tincture for each brother. In subsequent generations the bordure may be divided in two tinctures; the edge of the bordure, or of an ordinary in the base coat, may be changed from straight to indented, engrailed or invected; small charges may be added. These variations allow the family tree to be expressed clearly and unambiguously.

Because of the Scottish clan system, only one bearer of any given surname may bear plain arms. Other armigerous persons with the same surname have arms derived from the same plain coat, though (if actual kinship cannot be established) they must be differenced in a way other than the cadency system mentioned above. This is quite unlike the English system, in which the surname of an armiger is generally irrelevant.

Canadian cadency generally follows the English system. However, since in Canadian heraldry a coat of arms must be unique regardless of the bearer's gender, Canada has developed a series of brisures for daughters unique to Canada:^[5]

• for the first daughter, a heart;
• for the second daughter, an ermine spot;
• for the third daughter, a snowflake;
• for the fourth daughter, a fir twig;
• for the fifth daughter, a chess rook
• for the sixth daughter, an escallop (scallop shell);
• for the seventh daughter, a harp;
• for the eighth daughter, a buckle;
• for the ninth daughter, a clarichord.

Arms of the Queen	Arms of the Prince of Wales	Arms of Prince William	Arms of Prince Harry	Arms of the Duke of York	Arms of Princess Beatrice
Arms of Princess Eugenie	Arms of the Earl of Wessex	Arms of the Princess Royal	Arms of the Duke of Gloucester	Arms of the Duke of Kent	Arms of Prince Michael

There are no actual "rules" for members of the Royal Family, because they are theoretically decided ad hoc by the sovereign. In practice, however, a number of traditions are practically invariably followed. At birth, members of the Royal Family have no arms. At some point during their lives, generally at the age of eighteen, they may be granted arms of their own. These will always be the arms of dominion of the Sovereign with a label argent for difference; the label may have three or five points. Since this is in theory a new grant, the label is applied not only to the shield but also to the crest and the supporters to ensure uniqueness. Though de facto in English heraldry the crest is uncharged (although it is supposed to be in theory), as it would accumulate more and more cadency marks with each generation, the marks eventually becoming indistinguishable, the crests of the Royal Family are always shown as charged.

The Prince of Wales uses a plain white label. Traditionally, the other members of the family have used a stock series of symbols (cross of Saint George, heart, anchor, fleur-de-lys, etc.) on the points of the label to ensure that their arms differ. The labels of Princes William and Harry have one or more scallop shells taken from the arms of their mother, Diana, Princess of Wales^[6]; this is sometimes called an innovation but in fact the use of maternal charges for difference is a very old practice, illustrated in the "border of France" (azure semé-de-lys or) borne by John of Eltham, Earl of Cornwall (1316-36), younger son of Edward II of England and Isabella of France.

It is often said that labels argent are a peculiarly royal symbol, and that eldest sons outside the royal family should use labels of a different colour, usually gules.

First son	Second son	Third son	Fourth son	Fifth son	Sixth son	Seventh son	Eighth son
Label	Crescent	Mullet	Martlet	Annulet	Fleur-de-lys	Rose	cross moline [7]

Arms of the Dauphin of France	Arms of the Duke of Orléans	Arms of the Duke of Anjou	Arms of the Duke of Berry	Arms of the Prince of Condé	Arms of the Prince of Conti	Arms of the Herzog von Vendôme[8]

Arms of the Monarch	Arms of the Crown Prince of Portugal	Arms of the Prince of Beira	Arms of the First Infante of Portugal	Arms of the Second Infante of Portugal	Arms of the Third Infante of Portugal

First son	Second son	Third son	Fourth son	Fifth son	Sixth son	Seventh son
Undifferenced arms	Label	Crescent	Mullet	Martlet	Annulet	Fleur-de-lys[9]

Arms of King	Arms of Prince of Asturias	Arms of the Duchess of Lugo	Arms of the Duchess of Palma	Arms of the Duchess of Badajoz	Arms of the Duchess of Soria andHernani <ref>Template:Es icon La Brisura en la Casa Rela - Blog de Heraldica (April 18, 2009)