Person
The classical definition of a person is "a human being regarded as an individual."  In modern usage, the term "person" is subject to dispute and re-interpretation based on alternate definitions. This is especially so for uses that are not necessarily synonymous with the classical definition of human or human being.
For example, in many jurisdictions a corporation may be treated as a "person"  under the law. In the fields of philosophy, theology, and bioethics, the definition of 'person' may exclude human beings who are incapable of certain kinds of thought (such as embryos, fetuses with incomplete brain development, or adult humans lacking higher brain functions).
These alternative definitions of what constitutes a "person" include a  wide and varying range of alternative defining characteristics, some of which have evolved historically, and continue to shift with time and social context. Some other characteristics used to define a 'person' include personal identity, self-awareness, individuality, and a sense of self that persists through time. Other views centre around the degree to which properties such as agency (both human agency and moral agency) and rights are recognized and acknowledged in society or enforcable by law. The recognition of status as a person is known as personhood.
The inquiry into what it means to be a 'person' is the subject of considerable analysis and debate within diverse fields such as religion, medicine, ethics, economic and political theory, human rights, and animal rights.

# Overview
The establishment of 'personhood' represents a complex issue that covers a wide swath of human activities and discourse. Generally, the issue can be categorized by the underlying intended uses of the term "person".
Such intended uses include:
- Analytic: definitions or prescriptive rules used to delineate personhood in a falsifiable formal system;
- Normative: moral or deontological arguments to advocate fair and equitable treatment for recognized classes of sentient beings;
- Conceptual: descriptive, taxonomical, or epistemological inquiry into the fundamental nature, limitations, and scope of personhood; especially as it relates to the examination of living organisms or other intelligences;
- Metaphysical: esoteric or mystical exposition of personhood; especially as it relates to religion, spirituality, or mythical views and beliefs outside ordinary human experience
- Artistic: literary, rhetorical or allegorical devices to convey personhood; especially as it relates to fantasy and science fiction
Discourse on personhood may combine different elements of the previous categories in order to coincide with a particular viewpoint or academic theory. For example, a legal scholar and economist might define a person as "any being with the neurological prerequisites to understand moral consequences and take his life morally seriously." (Markovits)  The conceptual and normative elements could then be incorporated into established legal doctrine and economic theory, both of which assume some level of individual choice and personal responsibility.
The normative principle of absolutism is often combined with an analytic definition of persons as co-equal participants in a given society, based on citizenship, nationality or common humanity. This combination is very common in such instruments as the Declaration of the Rights of Man and of the Citizen, and the Universal Declaration of Human Rights.

## Analytic definitions
A person can have recognition, existence and legal capacity under the law (legal personhood). There are various legally operative definitions for personhood, but they all rely on formal, prescriptive definitions that must eventually be evaluated and falsifiable. Most such definitions form the basis of specific rights that may be exercised or enforced (such as human rights, custody, conservatorship and suffrage). Such definitions may also impose obligations or duties which carry a penalty if they are breached.
Some legally operative definitions of 'person' go beyond the scope of establishing rights and obligations for individual human beings. For example, in many jurisdictions, any artificial legal entity (like a school, business, or non-profit organization) is considered a juristic person.  As another example, the United States Constitution has historically applied different definitions of 'person' for the purpose of allotting seats in the House of Representatives.

## Normative views
Recognition as a 'person' is significant in society because it goes to the heart of many debates over the status, respect, rights, and treatments, which are obligatory to different types of living beings. It is closely connected to the societal concept that sufficiently intelligent or self-aware beings should be respected and have their rights enforced for this reason, whereas a degree of exploitation is permissible for entities lacking it. Such exploitation has at times taken the form of slavery or medical torture for humans, and cruelty and vivisection for animals. Personhood is directly connected to issues such as rights and the capability to protect those rights by law or to have them protected on one's behalf if incapable.

## Conceptual views
Human beings represent the most prevalent conceptual definition of 'person'. Some philosophers, like Peter Singer of Princeton University, regard certain types of animals with high cognitive abilities and a degree of societal development as persons, and argue that some human beings  for example, those with certain types of brain damage  are not. Should other intelligent life ever be discovered beyond those known to science, similar questions would be relevant in establishing personhood.

## Metaphysical views
Personhood is held by some to be an attribute of more than just human beings. Some religions specify deities as occupying the place of personhood in many different forms. It is not uncommon for spiritual and archetypal roles to be depicted as "persons".
For example, in the Book of Proverbs the attribute Wisdom is personified:
Scripture scholars differ on whether and the extent to which this and other similar personification represents an attribute of the Divine Nature as made manifest in the form of a distinct 'person'.

## Artistic depictions
Personhood is frequently examined through any of several artistic modalities, especially in literary works. In fictional works, fantasy and science fiction often explore the question of personhood by relaxing one or more of the common characteristics associated with it, and then exploring the ramifications and possible consequences. For example, Isaac Asimov introduced the three laws of robotics by relaxing the assumption that personhood is restricted to biological organisms. As another example, David Brin explored the attributes of personhood; especially identity, autonomy, and agency, by depicting a world in which characters could "copy" themselves in the novel Kiln People.  An notable example if the character Data from Star Trek: The Next Generation.  In one episode Data's status as a legal person was question and a hearing was carried out to determine if Data, an android who lacked human emotions but otherwise met or exceeded all other human mental characteristics such as self-awareness, imagination, creativity etc qualified as a person.

# Personhood in philosophy and theory
Philosophers have expounded on every dimension  from the purely analytical to the metaphysical  in discourses on personhood. Conceptually, a person is defined by the characteristics of reasoning, consciousness, and persistent personal identity. The English philosopher John Locke defined a person as "a thinking intelligent Being, that has reason and reflection, and can consider it self as it self, the same thinking thing in different times and places; which it does only by that consciousness, which is inseparable from thinking, and as it seems to me essential to it" (Essay on Humane Understanding, Book 2, Chapter 27, Section 9).

## Personhood theory
According to Boethius:
John Locke emphasized the idea of a living being that is conscious of itself as persisting over time (and hence able to have conscious preferences about its own future).
In recent years a kind of consensus among secular scholars has emerged, which might be referred to as "personhood theory". This is strongly influenced by Locke's approach. The criteria a person must have in being a person are one or more of the following:
- Consciousness,
- The ability to steer one's attention and action purposively,
- Self-awareness, self-bonded to objectivities (existing independently of the subject's perception of it),
- Self as longitudinal thematic identity, one's biographic identity.
Neo-Kantian philosophers over the last two decades have emphasized that conscious awareness requires both:
- The sensorial capacity to access an environment (and one's own body) in a way that offers the basic qualitative content for subjective experience.
- The intellectual capacity to conceptually interpret sensorial content as representing some thing to oneself.
Both of these capacities are required for a subject of experience, action, thought, or self-reflection to exist, at least in the physically embodied, world-accessing manner of humans (and presumably other intelligent animals). As Kant wrote:
Without sensibility no object would be given to us, and without understanding none would be thought. Thoughts without content are empty, intuitions without concepts are blind. (Critique of Pure Reason, A 51 = B 75).
For those who consider an embodied capacity for subjectivity as necessary for personhood, these abstract constraints are quite relevant to the personhood theory debate. Advocates of alternative positions, such as a biological species or potentiality criterion, would instead need to provide arguments against embodied subjectivity as a basis for personhood. For example, one might argue that property claims are made by immaterial minds on immature material bodies, though any claim as to the nature of such minds would be necessarily speculative and would typically involve an argument for Cartesian substance dualism (see "mind-body problem").
In addition speculatively, there are three other likely categories of beings where personhood might be at issue:
- Unknown intelligent life-forms - for example, should alien life be found to exist, under what circumstances would they be counted as 'persons'?
- Artificial life - at what point might human-created life be considered to have achieved 'personhood'?
- Artificial intelligence - assuming the eventual creation of an intelligent and self-aware system of hardware and software, what criteria would be used to confer or withhold the status of 'person'?
- Modified living beings - for example, how much of a human being can be replaced by artificial parts before personhood is lost?
- Further, if the brain is the reason people are considered 'persons', then if the human brain and all its thought patterns, memories and other attributes could also in future be transposed faithfully into some form of artificial device (for example to avoid illness such as brain cancer) would the patient still be considered a 'person' after the operation?
Such questions are used by philosophers to clarify thinking concerning what it means to be 'human', or 'living', or a 'person'.

# Implications of the person, non-person debate
The personhood theory has become a pivotal issue in the interdisciplinary field of bioethics. While historically most humans did not enjoy full legal protection as "persons" (women, children, non-landowners, minorities, slaves, etc.), from the late 18th through the late 20th century being born as a member of the human species gradually became secular grounds for an appeal for basic rights of liberty, freedom from persecution, and humanitarian care.
Since modern movements emerged to oppose animal cruelty (and advocate vegetarian or vegan lifestyles) and theorists like Turing have recognized the possibility of artificial minds with human-level competence, the identification of personhood protections exclusively with human species membership has been challenged. On the other hand, some proponents of "human exceptionalism" (also referred to by its critics as "speciesism") have countered that we must institute a strict demarcation of personhood based on species membership in order to avoid the horrors of genocide (based on propaganda dehumanizing one or more ethnicities) or the injustices of forced sterilization (as occurred in the U.S. to people with low I.Q. scores and prisoners).
While the former advocates tend to be comfortable constraining personhood status within the human species based on basic capacities (e.g. excluding human stem cells, fetuses, and bodies that cannot recover awareness), the latter often wish to include all these forms of human bodies even if they have never had awareness (which some would call "pre-people") or had awareness, but could never have awareness again due to massive and irrecoverable brain damage (some would call these "post-people"). The Vatican has recently been advancing a human exceptionist understanding of the personhood theory, while other communities such as Christian Evangelicals in the U.S. have sometimes rejected the personhood theory as biased against human exceptionism. Of course, many religious communities (of many traditions) view the other versions of the personhood theory perfectly compatible with their faith, as do the majority of modern Humanists.
The theoretical landscape of the personhood theory has been altered recently by controversy in the bioethics community concerning an emerging community of scholars, researchers and activists identifying with an explicitly Transhumanist position, which supports morphological freedom even if a person changed so much as to no longer be considered members of the human species (whatever standard is used for this determination).

# Individual rights and responsibility
Closely related to the debate on the definition of personhood is the relationship between persons', individual rights, and ethical responsibility. Many philosophers would agree that all and only people are expected to be ethically responsible, and that all people deserve a varying degree of individual rights. There is less consensus on whether only people deserve individual rights and whether people deserve greater individual rights than non-people. The rights of animals are an example of contention on this issue.

# Nonhuman sentient beings as persons
The idea of extending personhood to all animals has the support of legal scholars such as Alan Dershowitz and Laurence Tribe of Harvard Law School, and animal law courses are now taught in 92 out of 180 law schools in the United States. On May 9, 2008, Columbia University Press will publish Animals as Persons: Essays on the Abolition of Animal Exploitation by Prof. Gary L. Francione of Rutgers University School of Law, a collection of writings that summarizes his work to date and makes the case for non-human animals as persons.
There are also hypothetical persons, sentient non-human persons such as sentient extra-terrestrial life and self aware machines. A popular Novel and loosely based animated series called Ghost in the Shell frequently touches on the potential of inorganic sentience, while classical works of fiction and fantasy regarding extra-terrestrials have challenged people to reconsider long held traditional definitions.