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Degrees of consanguinity chart: civil and canon law counting

A degree of consanguinity counts generations between blood relatives. The chart gives civil and canon degrees for parents, siblings, cousins and more.

Portrait of Elspeth GilchristElspeth Gilchrist · · 8 min read
Degrees of consanguinity chart: civil and canon law counting

A degree of consanguinity measures how closely two blood relatives are related by counting generations. The civil-law method counts every step from one person up to the nearest shared ancestor and back down to the other, so first cousins are related in the fourth degree. The traditional canon-law method counts only the longer of the two lines, so first cousins are in the second degree.

Consanguinity means relationship by descent from a shared ancestor. Its partner term, affinity, means relationship through a marriage, and it is counted from the same chart, as shown further down. First, the chart itself.

The chart

Each relative is placed by two counts: how many generations each person sits below the nearest ancestor they share. For a parent and child the parent is that ancestor, so the counts are 0 and 1.

Relationship (either direction) Generations below the shared ancestor Civil degree Traditional canon degree
parent and child 0 and 1 1 1
grandparent and grandchild 0 and 2 2 2
siblings, full or half 1 and 1 2 1
great-grandparent and great-grandchild 0 and 3 3 3
aunt or uncle and niece or nephew 1 and 2 3 2
great-aunt or great-uncle and grandniece or grandnephew 1 and 3 4 3
first cousins 2 and 2 4 2
great-great-aunt or uncle and great-grandniece or nephew 1 and 4 5 4
first cousins once removed 2 and 3 5 3
first cousins twice removed 2 and 4 6 4
second cousins 3 and 3 6 3
second cousins once removed 3 and 4 7 4
second cousins twice removed 3 and 5 8 5
third cousins 4 and 4 8 4

The same chart can be read the other way round, listing who falls in each civil degree. This is how Justinian's Institutes arranged the subject, degree by degree up to the sixth:

Civil degree Relatives in that degree
1 parents, children
2 grandparents, grandchildren, siblings
3 great-grandparents, great-grandchildren, aunts and uncles, nieces and nephews
4 great-great-grandparents and great-great-grandchildren, great-aunts and great-uncles, grandnieces and grandnephews, first cousins
5 3rd great-grandparents and 3rd great-grandchildren, great-great-aunts and uncles, great-grandnieces and nephews, first cousins once removed
6 4th great-grandparents and 4th great-grandchildren, 3rd great-aunts and uncles, great-great-grandnieces and nephews, first cousins twice removed, second cousins

Every figure in both tables matches our cousin calculator, which reports both counts for any pair of generation numbers up to twelve.

How to count

Start by finding the nearest shared ancestor. For siblings it is a parent, for first cousins a grandparent, for second cousins a great-grandparent. Then count the parent and child links down each line.

  • Civil count: add the two lines.
  • Traditional canon count: take the longer line.

In the direct line the two methods agree, because one of the lines has length zero: a great-grandparent is three generations from a great-grandchild by either count. They part company in the collateral line, among relatives who share an ancestor without descending from each other.

Three worked examples:

  1. Great-aunt and grandniece. The great-aunt is a child of the shared couple (1), and the grandniece is their great-grandchild (3). Civil: 1 + 3 = 4. Canon: the longer line, 3.
  2. First cousins once removed. Lines of 2 and 3. Civil: 2 + 3 = 5. Canon: 3.
  3. Second cousins twice removed. Lines of 3 and 5. Civil: 3 + 5 = 8. Canon: 5.

Half relationships keep the same degree. Half siblings share one parent rather than two, but the lines are still one generation each, so they stand in the second civil degree and the first canonical one. The difference between full and half shows up in genetic relatedness, not in the degree count.

Where the two methods came from

The civil method is Roman. Justinian's Institutes, a law textbook issued at Constantinople on 21 November 533, devotes a title to the degrees of cognation. It places siblings in the second degree, first cousins in the fourth and second cousins in the sixth, notes that each generation adds one degree, and remarks that stating the degree is far easier than finding the right name for the relative. The text says a table was inserted so students could learn the degrees by eye as well as by ear, which makes the consanguinity chart a teaching aid with a very long pedigree. The same book allowed the children of two siblings to marry.

The canonical method came later. According to Richard Burtsell's 1908 article on consanguinity in the Catholic Encyclopedia, Pope Alexander II (1061 to 1073) treated the one-line count as church law, and some writers called it the Germanic computation because it resembled a Germanic way of reckoning inheritance. Because it roughly halves the number for collateral relatives, any ban expressed in degrees reached much further under it. A prohibition to the fourth degree meant first cousins under the civil count and third cousins under the canonical one, and the Fourth Lateran Council of 1215 limited the marriage impediment to that canonical fourth degree. Burtsell also notes that, outside marriage, canon law used the civil count, for instance for inheritance.

The modern Catholic code has changed the count. Canon 108 of the 1983 Code of Canon Law says that in the collateral line there are as many degrees as there are persons in both lines together, not counting the common ancestor, which gives the civil number. Canon 1091 makes marriage invalid in the collateral line up to and including the fourth degree, so the line now falls at first cousins, and canon 1078 rules out any dispensation for the direct line or for the second degree of the collateral line (siblings). The cousin calculator shows the traditional longer-line count alongside the civil one, so check which count a document means before comparing numbers.

Consanguinity and affinity

Affinity is the tie created by marriage between one spouse and the other spouse's blood relatives. Both the canon code and some civil statutes count it with the consanguinity chart. Canon 109 says that the wife's blood relatives are related to the husband by affinity in the same line and degree, and the reverse. Texas uses the same idea in its nepotism law: section 573.025 of the Texas Government Code puts husband and wife in the first degree of affinity and gives every other affinity tie the degree of the blood tie underneath it.

Relative by marriage Blood tie underneath Degree of affinity (civil count)
spouse's parent spouse and parent: 1st degree 1
spouse's sibling spouse and sibling: 2nd degree 2
sibling's spouse you and your sibling: 2nd degree 2
spouse's grandparent 2nd degree 2
spouse's niece or nephew 3rd degree 3
spouse's first cousin 4th degree 4

Affinity does not chain. Your spouse's sister's husband is not related to you by affinity under either definition, because neither of you is a blood relative of the other's spouse. Texas also says when affinity ends: section 573.024 ends it with divorce or a spouse's death unless a child of that marriage is living.

Degrees in law today

Statutes use these counts in two different ways. Some name a degree and say which count to use. Texas Government Code section 573.021 says degrees are "computed by the civil law method", and section 573.002 applies the state's nepotism rules to relatives within the third degree by consanguinity or the second by affinity. Section 573.023 then spells the third degree out by name: great-grandparents and great-grandchildren, aunts and uncles, nieces and nephews. By that count a first cousin, in the fourth degree, sits one step past the line the chapter draws.

Other laws skip degrees and list relationships. Section 6.201 of the Texas Family Code makes a marriage void between ancestor and descendant, brother and sister, a person and a parent's brother or sister, and a person and a brother's or sister's child, whether of the whole or half blood or by adoption. In England and Wales, Schedule 1 of the Marriage Act 1949 does the same with a short list of kindred (parent, child, grandparent, grandchild, sibling including half-sibling, parent's sibling, sibling's child, plus adoptive and former adoptive parent and child) and a separate list of relatives by affinity.

Marriage law varies a great deal between US states and between countries, and it changes. The examples above show how statutes count, nothing more. They are not legal advice and do not answer whether any particular marriage, appointment or inheritance is allowed. For a real question, read the current text that applies where you live and ask a lawyer licensed there.

What a degree can and cannot tell you

The civil degree carries more information than it seems to. For the people in the chart it fixes Wright's coefficient of relationship r, the expected share of DNA two relatives have in common by descent, once you know the kind of tie. Write d for the civil degree:

  • direct line: r = (1/2)^d
  • full collateral relatives, descended from a couple: r = 2 × (1/2)^d
  • half collateral relatives, descended from one shared person: r = (1/2)^d

First cousins are in the fourth civil degree with a couple as the shared ancestors, so r = 2 × (1/2)^4 = 1/8. A great-great-grandparent is also in the fourth degree, but in the direct line, so r = (1/2)^4 = 1/16.

The traditional canon degree throws that information away. Its third degree holds a great-aunt (r = 1/8), a great-grandparent (1/8), a first cousin once removed (1/16) and a second cousin (1/32): a fourfold spread under one number. For the arithmetic behind r, see the worked examples of the coefficient of relationship, and for the two cousin cases most often confused, first cousin once removed vs second cousin and second cousin once and twice removed. Enter 3 and 5 in the calculator and it returns a second cousin twice removed: civil degree 8, canon degree 5, r = 1/128.

Sources and further reading

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