Cousin

Family tree showing the relationship of each person to the orange person. Cousins are colored green. Generations are shown by alternating stripes of gray and white.

In kinship terminology, a cousin is a relative with whom one shares a common ancestor. In modern usage, the term is rarely used when referring to a relative in one's own line of descent, or where there is a more specific term to describe the relationship: e.g., brother, sister, aunt, uncle. The term blood relative can be used synonymously, and underlines the existence of a genetic link.

A system of degrees and removes is used to describe the relationship between the two cousins and the ancestor they have in common. The degree (first, second, third cousin, etc.) indicates one less than the minimum number of generations between either cousin and the nearest common ancestor; the remove (once removed, twice removed, etc.) indicates the number of generations, if any, separating the two cousins from each other.

For example, a person with whom one shares a grandparent (but not a parent) is a first cousin; someone with whom one shares a great-grandparent (but not a grandparent) is a second cousin; and someone with whom one shares a great-great-grandparent (but not a great-grandparent) is a third cousin; and so on. The child of one's first cousin is one's first cousin once removed because the one generation separation represents one remove. Oneself and the child are still considered first cousins, as one's grandparent (this child's great-grandparent), as the most recent common ancestor, represents one degree.

Non-genealogical usage often eliminates the degrees and removes, and refers to people with common ancestors merely as cousins or distant cousins. Alternatively, the terms 'second cousin' and 'first cousin once removed' are often incorrectly used interchangeably.

The system can handle kinships going back any number of generations (subject to the genealogical information being available).

Cousin chart

A cousin chart, or table of consanguinity, is helpful in identifying the degree of cousin relationship between two individuals using their most recent common ancestor as the reference point. Cousinship between two individuals can be specifically described in degrees and removes by determining how close, generationally, the common ancestor is to each individual.

Additional modifying words are used to clarify the exact degree of relatedness between the two people. Ordinal numbers are used to specify the number of generations between individuals and a common ancestor, and further clarification of exact cousinship is made by specifying the difference in generational level between the two cousins, if any, by using degrees of remove. For example, "first cousins once removed" describes two individuals with the common ancestor being the grandparent of one cousin (one degree) and the great-grandparent of the other cousin. The cousins themselves are one generation different from each other (one remove).

If one person's →		Grandparent	Great-grandparent	Great-great-grandparent	Great3-grandparent	Great4-grandparent	Great5-grandparent
is the other person's ↓	then they are ↘
Grandparent		1st cousins	1st cousins once removed	1st cousins twice removed	1st cousins thrice removed	1st cousins four times removed	1st cousins five times removed
Great-grandparent		1st cousins once removed	2nd cousins	2nd cousins once removed	2nd cousins twice removed	2nd cousins thrice removed	2nd cousins four times removed
Great-great-grandparent		1st cousins twice removed	2nd cousins once removed	3rd cousins	3rd cousins once removed	3rd cousins twice removed	3rd cousins thrice removed
Great3-grandparent		1st cousins thrice removed	2nd cousins twice removed	3rd cousins once removed	4th cousins	4th cousins once removed	4th cousins twice removed
Great4-grandparent		1st cousins four times removed	2nd cousins thrice removed	3rd cousins twice removed	4th cousins once removed	5th cousins	5th cousins once removed
Great5-grandparent		1st cousins five times removed	2nd cousins four times removed	3rd cousins thrice removed	4th cousins twice removed	5th cousins once removed	6th cousins

Chart relationships as sentences

Reminder: the closest relationship prevails — note that cousinship is not calculated between individuals when one is descended from the other; for example, two individuals are not called cousins if they are any degree of grandparent, parent or child. Also, cousinship is not calculated between individuals of any degree of aunt/uncle and nephew/niece relationship to each other.

• If we share the same parents we are siblings
• If we share grandparents but have different parents we are first cousins
• If we share great-grandparents but have different grandparents we are second cousins
• If my grandparents are your great-grandparents (or vice versa) we are first cousins once removed

---

• My parent's sibling is my aunt/uncle
• My grandparent's sibling is my grandaunt/granduncle or great-aunt/-uncle

Similarly

• My sibling's child is my nephew/niece
• My sibling's grandchild is my grandnephew / grandniece

---

• My first cousin's child and I are first cousins once removed (one generation difference between us)
• My first cousin's grandchild and I are first cousins twice removed (two generations difference between us)

Similarly

• My parent's first cousin and I are first cousins once removed (one generation difference between us)
• My grandparent's first cousin and I are first cousins twice removed (two generations difference between us)

---

• My second cousin's child and I are second cousins once removed (one generation difference between us)
• My second cousin's grandchild and I are second cousins twice removed (two generations difference between us)

Similarly

• My parent's second cousin and I are second cousins once removed (one generation difference between us)
• My grandparent's second cousin and I are second cousins twice removed (two generations difference between us)

---

• My third cousin's child and I are third cousins once removed (one generation difference between us)
• My third cousin's grandchild and I are third cousins twice removed (two generations difference between us)

Similarly

• My parent's third cousin and I are third cousins once removed (one generation difference between us)
• My grandparent's third cousin and I are third cousins twice removed (two generations difference between us)

---

Following this pattern, it can be determined that xth cousin y-times removed means either of the following:

• The xth cousin of your direct ancestor y generations previously (e.g. your great-grandparent's fifth cousin is your fifth cousin thrice removed); or
• Your xth cousin's direct descendant y generations away (e.g. your fifth cousin's great-grandchild is also your fifth cousin thrice removed)

Determining cousin type

The name of the cousinship is not determined by oneself, but rather is always determined by the generational level of the individual most closely related to the ancestor in common. The following assumes there are no double cousins:

1. To work out if two people are first, second, or third cousins, count back the generations to their common ancestor. For example, if the common ancestor is one's grandmother, that is two generations. If it is one's great-grandmother, that is three generations.
2. Identify the one of the two descendants who is generationally closest to the common ancestor. For example, if one of the cousins is a great-great-grandchild (four generations) and the other is a grandchild, the grandchild is generationally closest to the common ancestor.
3. If the generationally closest descendant of the common ancestor is a grandchild (two generations), then the cousins are first cousins; if three generations separate the common ancestor and the generationally closest cousin, then the two are second cousins, and so on.
4. If the cousins are separated from the common ancestor by an equal number of generations, there is no "remove," for instance if both are grandchildren of the common ancestor. But if the number of generations between the common ancestor is different for each cousin, that difference is expressed by using a clarifier, "removed," with the number of removes. For example, if one person is a grandchild of (2 generations from) the common ancestor, and the other person is a great-great-grandchild of (4 generations from) that common ancestor, then the two are first-cousins-twice-removed.

An alternative method is as follows. You and your cousin count the generations between you and the common ancestor. Do not count the common ancestor and do not count yourselves. Thus, if it is a grand parent, this number is one. Let this be X. If X is different for the two of you, then let the difference between be Y. Now, use the smaller X (if there is a difference). You are X cousins, Y times removed. If Y is zero (because the number of generations between you and your ancestor is the same as for your cousin), then you are simply X cousins. X is stated as an ordinarial, i.e. first, second, etc.

Note that the above system is symmetric; if person A is person B's second cousin once removed, then person B is person A's second cousin once removed as well, even though the relationship between them is not symmetric (since the two are not from the same generation).

Also note that much of this terminology is variable; for example, many dictionaries give "a child of one's first cousin" as an incorrect secondary sense for the term second cousin (the primary sense being "a child of a first cousin of one's parent").

A different and partly conflicting system that is sometimes used is asymmetric (i.e. it mirrors the fact that aunt/uncle and niece/nephew are asymmetric names). With this system to work out what cousinage X is to Y, identify the descendant or ancestor of X that is the same generation as Y (i.e. the same number of generations from the common ancestor), then count how many generational removes there are up or down the tree from those same-generation cousins. In other words go across the family tree first, then up or down. For example take X and Y who have common ancestors who are X's great-grandparents and Y's grandparents. From Y's point of view, X is Y's first cousin's child, and thus is Y's first cousin once removed (downwards), but from X's point of view Y's child is X's second cousin, and Y therefore is X's first cousin once removed (upwards).

Double cousins

Generally, one's cousinship to another is determined by a connection through only one parent's biological family. But an individual's cousinship to another individual may be determined by a connection through both of one's parents. These cousins are biologically connected to both the maternal and paternal family trees and that cousinship is termed a double cousin. Another term used to describe this is cousins on both sides.

If a pair of siblings from one family each form a couple with a pair of siblings from another family, then the children of these two couples will be double first cousins to one another. The children of the couples would already automatically be first cousins because they are children of one of their parent's siblings, but in this case the children of their mother's sibling are also the children of their father's sibling, and thus they are double first cousins. Such cousins have double the consanguinity of ordinary cousins and are as related as half-siblings. Instead of the 12.5% consanguinity that simple first cousins share with each other, double first cousins share a 25% consanguinity with each other. Further, when identical twins form a coupling with a corresponding set of identical twins, the children of these two couples, though legally (double) first cousins to one another, would genetically be as closely related to each other as ordinary full siblings.

Other types of cousins

When identical twins reproduce with the same person, the resulting children are likewise genetically indistinguishable from full siblings, although they are legally half-siblings and first cousins. When identical twins reproduce with siblings the resulting children are more related than half-siblings but less related than full siblings. When two siblings who are not identical twins marry the same person, the resulting children are likewise more related than half-siblings but less related than full siblings. The same situation arises when two half-siblings marry the same person. Children of double first cousins are double second cousins to each other.

Chart relationships as sentences:

• If two first cousin men have children with two first cousin women then these children are double second cousins because they share both sets of great-grandparents on both the maternal and the paternal family trees.

• If two female first cousins have children with two male second cousins, these children are maternal second cousins / paternal third cousins.

• If two siblings procreate with two second cousins then the resulting children would be paternal first cousins and maternal third cousins, or vice versa.

• Inbreeding: If a male and a female third cousins have children, then these children would be siblings / double fourth cousins. (See cousin marriage.) This could be construed as incest in some cultures, especially if the third cousins know that they are related. Technically, it is considered inbreeding as geneticists can easily detect a genetic relationship with third cousins.

• If a male and a female second cousins have children with siblings a brother and sister and then these children are first cousins / double third cousins.

Half-cousins

Half-siblings share only one parent. Extrapolating from that, if one of John's parents and one of Mary's parents are half-siblings, then John and Mary are half-first cousins. The half-sibling of each of their respective parents would be their half-aunt or half-uncle but these terms, although technically specific, are rarely used in practice. While it would not be unusual to hear of another's half-brother, or half-sister, so described, in common usage one would rarely hear of another's half-cousins or half-aunt, so described, and instead hear them described simply as the other's cousin or aunt. Also, children of half-first cousins are half-second cousins to each other and so on because they would share only one common great-grandparent out of eight instead of two, and so on.

One-and-a-half-cousins

One and a half cousins may be produced when two full siblings have children with two half-siblings. However, if a set of half-siblings has children with another set of half-siblings, the resulting children would be double-half first cousins, and would have the same consanguinity as full first cousins. Furthermore, if a person's half-sibling marries the person's half-sibling from the other parent, assuming they are not step-siblings, then the child of that couple and the child of the half-sibling who is related to both partners in the married couple will likewise be double-half first cousins.

Step-cousins

Step-cousins are either stepchildren of an individual's aunt/uncle, or children of a step-aunt/uncle. This term is used only to promote family unity, as no blood relationship exists between step-cousins, although there does not need to be a "blood" relationship between cousins as in the case of one or both of the siblings being adopted, their children would still be first cousins. Step first cousins once removed would be the stepchildren of your first cousins. Step 2nd cousins are when someones first cousin once removed gets married to a individual and that individual's child is the step 2nd cousin.

Cousin-in-law

A cousin-in-law is the spouse of an individual's cousin, similarly the cousin of an individual's spouse.

Cousin from mother/father side

Everybody may have cousins from his/her mother's or father's side for example: Tina is Jim's cousin from his Mother's side and John is Jim's cousin from his Father's side. Tina and John are not related to each other but both of them are Jim's cousins.

In Chinese kinship, among other systems, the terms for cousins related through only paternal relationships are different.

Mathematical definitions

The family relationship between two individuals a and b, where G_a and G_b respectively are the number of generations between each individual and their nearest common ancestor, can be calculated by the following:

x = min (G_a, G_b)

y = |G_a − G_b|

• If x = 0 and y = 0 then they are the same person.
• If x = 0 and y = 1 then they are parent and child.
• If x = 0 and y = 2 then they are grandparent and grandchild.
• If x = 0 and y > 2 then they are great ... great-grandparent and great ... great-grandchild, with y − 2 greats.

• If x = 1 and y = 0 then they are siblings (brothers, sisters or brother and sister).
• If x = 1 and y = 1 then they are uncle/aunt and nephew/niece.
• if x = 1 and y = 2 then they are granduncle/grandaunt and grandnephew/grandniece (or great-uncle/great-aunt and great-nephew/great-niece).
• If x = 1 and y > 2 then they are great ... great-granduncle/great-grandaunt and great ... great-grandnephew/great-grandniece, with y − 2 greats (or great- ... great-uncle/great- ... great-aunt and great- ... great-nephew/great- ... great-niece, with y − 1 greats).

• If x > 1 and y = 0 then they are x − 1st cousins. First cousins are usually just called cousins when contrast with more distant relations is not called for.
• If x > 1 and y > 0 then they are x − 1st cousins y times removed.

If x > 0 and they only share one nearest common ancestor rather than two, then the word "half" is sometimes added at the beginning of the relationship.

Granduncle/grandaunt and grandnephew/grandniece are equivalent to great-uncle/great-aunt and great-nephew/great-niece. Both great-uncle and granduncle refer to an uncle of one's father or mother. Neither form is definitively more correct than the other.

The mathematical definition is more elegant if you always express consanguinity as the ordered pair of natural numbers (x, y) as defined above. In that case, the relationship one has with oneself is (0, 0), the relationship between parent and child is (0, 1), and the relationship between grandparent and grandchild is (0, 2). The relationship between siblings is (1, 0); and between aunt/uncle and nephew/niece is (1, 1). First cousins are (2, 0). The first number expresses how many generations back the two people's most recent common ancestor is, while the second number expresses the generation difference between the two people.

Alternative canon law charts

Canon Law Relationship Chart. See an example of how to use chart.

Another visual chart used in determining the legal relationship between two people who share a common ancestor is based upon a diamond shape, and is usually referred to as a canon law relationship chart.

The chart is used by placing the "common progenitor" (the person from whom both people are descended) in the top space in the diamond shaped chart, and then following each line down the outside edge of the chart. Upon reaching the final place along the opposing outside edge for each person, the relationship is then determined by following that line inward to the point where the lines intersect. The information contained in the common "intersection" defines the relationship.

For a simple example, in the illustration to the right, if two siblings use the chart to determine their relationship, their common parents are placed in the topmost position and each child is assigned the space below and along the outside of the chart. Then, following the spaces inward, the two would meet in the "brother (sister)" diamond. If their children want to determine their relationship, they would follow the path established by their parents, but descend an additional step below along the outside of the chart (showing that they are grandchildren of the common progenitor); following their respective lines inward, they would come to rest in the space marked "1st cousin." In cases where one side descends the outside of the diamond further than the other side because of additional generations removed from the common progenitor, following the lines inward shows both the cousin rank (1st cousin, 2nd cousin) plus the number of times (generations) "removed."

In the example provided at the right, generations one (child) through ten (8th great-grandchild) from the common progenitor are provided; however the format of the chart can easily be expanded to accommodate any number of generations needed to resolve the question of relationship.

Alternative definitions

Sometimes, the term cousin can mean as "a person or thing related to another by similar natures, languages, geographical proximity" or "a term of address used by a sovereign in speaking, writing, or referring to another sovereign or a high-ranking noble."

See also

• Consanguinity
• Cousin couple
• Cross cousin
• Double first cousin
• Parallel cousin
• Collateral descendant
• Family
• Genealogical numbering systems
• Kinship terminology
• Most recent common ancestor

References

External links

• Genealogy.com definition of various cousins
• Genealogy.com: What makes a cousin?