[updated – see postscript below]
This essay summarizes the recent series of New York State cases that were filed by the Non Human Rights Project (NhRP) petitioning to have four chimpanzees released from their owners. NhRP’s primary intent was to have the chimpanzees recognized as human-like beings with a common law right to liberty — to be recognized as autonomous and self-determining beings that cannot be legally considered as property.  The summary includes a discussion on the Hohfieldian system of legal rights that was relied upon by the petitioners.
At the end of 2013 NhRP filed three separate writ of habeas corpus petitions on behalf of four chimpanzees — Tommy, Kiko, and Hercules and Leo. The chimpanzees were chosen from different areas of New York state so that they could be filed in different circuits, increasing the chances of a positive outcome. At the time of the filings Tommy was held inside a trailer at a place that rented trailers as well as animals, Kiko was owned by a primate specialist, and Hercules and Leo were held at a university laboratory for studies on human locomotion. 
The writ of habeas corpus allows an individual to assert his right to liberty and demand for release from unlawful imprisonment. It can be traced to 17th century England and it has progressed to US courts through common law — the practice of basing the current decision on previous decisions. The previous decisions are known as precedent, a legal term that encompasses all previous legal decisions and reasoning that can be considered to be relevant to the facts and circumstances at hand. This is considered to be an evolutionary process as there may be significant changes in interpretation of legal precedent due to changes in the circumstances surrounding the issue — historical changes in politics, economics, social issues and morality. The right to file the writ is protected in the US Constitution under Article 1, Section 9: “The privilege of the writ of habeas corpus shall not be suspended, unless when in cases of rebellion or invasion the public safety may require it.” Traditionally the writs are filed against the government and alleging illegal imprisonment.
The question of whether a chimpanzee can assert the right to liberty has not been previously considered by common law courts or addressed by the legislature. Consequently, NhRP’s strategy was to file habeas corpus petitions and show that if previous legal reasoning and principles were applied to what we now know about chimpanzees, then it should be recognized that they are autonomous human-like beings and can no longer be owned as private property. 
Under New York state law “a person illegally imprisoned or otherwise restrained with his liberty within the state … may petition without notice for a writ of habeas corpus to inquire into the cause of such detention and for deliverance.”  As its first step, NhRP argued that the legal term person is not a synonym for a human being, but instead refers to an entity with a capacity to possess legal rights. It emphasized that there are no necessary nor sufficient conditions for determining that an entity is a legal person. There are cases where human beings were not considered to be legal persons, not only pre-20th century human slavery cases, but also recent ones dealing with abortion. Those are cases where a fetus is not considered to be a person in the context of the 14th Amendment (“… nor shall any State deprive any person of life, liberty, or property, without due process of law”). On the other hand, there are cases going back to the 1800s where non human beings, like corporations, where found to have legal rights. Consequently, NhRP argued that the fact that a chimpanzee is not a human being should not prevent the argument that it is a legal person with a habeas corpus right to liberty. 
NhRP’s central point was that based on previous common law decisions, human autonomy and self-determination are the human qualities that are intended to be protected by the writ of habeas corpus. This is a narrow conception of liberty that NhRP defined as the right to bodily liberty. It argued that because chimpanzees are now known to possesses the same qualities, the right to bodily liberty should be expanded to this species.  More than thirty pages of the petition were devoted to going over chimpanzee evolutionary development, neurology, social practices and complex cognition.  All of this was based on attached documents from a dozen primatologists of various specializations. Below are a few of the listed qualities:
“Possession of an autobiographical self, episodic memory, self-determination, self-consciousness … empathy, a working memory, language, metacognition, numerosity, and material, social, and symbolic culture, their ability to plan … their ability to understand cause-and-effect and the experiences of others, to imagine, imitate … and to use and make tools.” 
As justification for the expansion of the right to chimpanzees, NhRP presented numerous 17th and 18th century England and New York state habeas corpus cases, where petitions were filed on behalf of human slaves. In many cases the slaves where considered as property, but nevertheless their petitions were accepted and their right to liberty was found to be violated, resulting in them being freed from their former owners. 
All three petitions were filed, with hearings being held for both Tommy and Kiko. At Tommy’s hearing the court made it very clear that the analogy to slavery would not be considered:
COUNSEL: … the famous case of Somerset vs. Stewart, which was 1772 England, a common law writ of habeas corpus case which was absorbed into the common law of New York when New York became a state. And that was for the first time you had a black slave who was seen as a legal thing, was able to come into court, went in front of…
COURT: Court’s not even going to consider that as synonymous, so you’ll have to use your other cases. I’m just telling you, the Court will reject that argument, the argument that the cases involving human-beings who were slaves in the 1800s as synonymous with a chimpanzee. I reject it. 
At Kiko’s hearing NhRP counsel emphasized that they were not seeking human rights for the chimpanzee and were only seeking a narrow expansion of bodily liberty. 
All three petitions where denied on the grounds that the chimpanzees where not persons and thus the issues in the petitions would not be considered. All three decisions were appealed. Tommy’s and Kiko’s appeals where accepted. Hercules and Leo’s appeal was denied on technical grounds, the petition was refiled and has not yet been reconsidered. At Kiko’s hearing the two main issues were: how would it be determined that a chimpanzee actually wanted to be released, and if it could be determined, would a transfer to another location be considered as a release from confinement, the purpose of the writ of habeas corpus. From Kiko’s hearing:
COURT: Part of the problem I’m having with your argument counsel, is that, and it is impressive — the experts, that announce that chimpanzees are autonomous, have self-determination… But it’s that self-determination itself that’s causing you problems, because, if that’s true, then a self-determination would not to be kept in another captive environment, it would be to be free. Your client [NhRP] would be determining for Kiko where Kiko lives, what Kiko gets in terms of food, exercise, you know, exposure to outdoors and indoors. All those determinations would be made by someone other than Kiko if your client gets the full relief.
COUNSEL: But, that, see, but that is going to have to be so when you’re dealing with someone who’s not an adult human being. The same thing happens with a child… the child cannot do whatever he wants. Someone else is going to make the call for him. But the important thing is that it’s the interests of the child that are being taken into account. And here, it would be the interests of Kiko that are being taken into account, not the interests of a person who calls himself his owner, and who has him with a chain around his neck in a cage…
COURT: How do we know he even wants to leave? 
NhRP’s counsel argued that such issues are regularly resolved in cases dealing with autonomous and self-determining human beings who at that time are incompetent or are too young to make those decisions. When asked by the court, the counsel answered that a chimpanzee is more akin to a young child around the age of five rather that a mentally retarded adult.
Kiko’s appeal was rejected. The court stated that even if a petition was considered, it would be denied because “this matter is governed by the line of cases standing for the proposition that habeas corpus does not lie where a petitioner seeks only to change the conditions of confinement rather than the confinement itself.”  Kiko is in the process of filing for a subsequent appeal. At Tommy’s hearing one of the main issues was concerned with the concept of rights and whether or not they are necessarily accompanied by responsibilities.
COURT: Well, but even you in your brief when you talk about individual rights, you talk about the fact that along with those individual rights come responsibilities, and we’re not, and you don’t want us to foist any responsibilities on this chimpanzee…
COURT: …you just want us to determine that he has the opportunity to be free of this confinement.
COUNSEL: The, the better way to view Tommy, would be similar to a human child who has, who has rights, you can’t put a little child in a cage, but doesn’t have correlative responsibilities. So Tommy has the autonomy and self-determination that is sufficient for him to be a legal person, and he can understand that he does not want to be imprisoned, for his life in a cage, which he has been. But he’s not going to be the um, defendant in a criminal action or a civil plaintiff, at least not, not by himself, they may have someone like the Non-Human Rights Project to come in… to um, to argue on his behalf. 
Tommy’s appeal was rejected. In its decision the court confirmed the earlier ruling that there is no precedent for finding that an animal could be thought of as a person. However, it reasoned further that:
“The lack of precedent for treating animals as persons for habeas corpus purposes does not, however, end the inquiry, as the writ has over time gained increasing use given its great flexibility and vague scope. While petitioner proffers various justifications for affording chimpanzees, such as Tommy, the liberty rights protected by such writ, the ascription of rights has historically been connected with the imposition of societal obligations and duties. Reciprocity between rights and responsibilities stems from principles of social contract, which inspired the ideals of freedom and democracy at the core of our system of government. Under this view, society extends rights in exchange for an express or implied agreement from its members to submit to social responsibilities. In other words, rights are connected to moral agency and the ability to accept societal responsibility in exchange for those rights.”
Black’s Law Dictionary defines the term “person” as “a human being” or, as relevant here, “an entity (such as a corporation) that is recognized by law as having the rights and duties of a human being.” It then goes on to provide: “So far as legal theory is concerned, a person is any being whom the law regards as capable of rights and duties … Persons are the substances of which rights and duties are the attributes. It is only in this respect that persons possess juridical significance, and this is the exclusive point of view from which personality receives legal recognition.”
“Needless to say, unlike human beings, chimpanzees cannot bear any legal duties, submit to societal responsibilities or be held legally accountable for their actions. In our view, it is this incapability to bear any legal responsibilities and societal duties that renders it inappropriate to confer upon chimpanzees the legal rights — such as the fundamental right to liberty protected by the writ of habeas corpus — that have been afforded to human beings.” 
NhRP has filed for an appeal to this decision. At the center of its argument is a reply to the court’s analysis of the concept of rights. NhRP’s argument is based on early 20th century writing of Wesley Hohfeld, a jurist whose work is considered to be fundamental to the modern conception of rights. Hohfeld pointed out that the term rights has multiple meanings with significant differences and that these meanings are often swapped for one another, producing major flaws in legal reasoning. Rights such as the right to property, a particular state’s right to bear arms or the constitutional right to an attorney are all combinations of the basic fundamental rights. There are four types of basic rights, with each right being a relationship between two correlating parties, with each party exercising an elementary legal concept.
There are two primary rights:
– A claims right is the basic right of a party to have the correlating party perform a duty.
– A privilege is the privilege of a party not to perform a duty because there is no-right for the correlating party to demand that a duty be performed.
And there are two secondary rights, which specify how a party can introduce, change and alter the primary rights:
– A power is the power of a party to alter the above primary rights of the correlating party. The correlating party has a liability to abide by an exercise of the power right.
– An immunity is the immunity of a party from having its claim rights or a privilege right altered by the correlating party. The correlating party has a disability preventing it from making those alterations. 
Under the current law, the right to property to possess a chimpanzee consists of multiple instances of all four of the Hohfeldian basic rights. Normally an owner has the privilege of keeping its possession at one location or moving it to another location, this is because there is no party with a right to which the owner has a duty to perform otherwise. There is an immunity that correlates to another party’s disability such as taking possession of the chimpanzee and moving it to another location or selling it to a third party. In contrast, the owner has the power to sell the chimpanzee to another party, creating a contract under which the correlating party takes on the liability of making the contract’s duties and benefits legally binding. Under the contract the owner has claim rights that the correlating party perform a specific duties, such as paying a specific amount before taking possession of the chimpanzee.
In its appeal NhRP argued that the court committed an error in requiring Tommy to be able to carry out legal duties in order to be considered a legal person with a right to bodily liberty. It quoted Hohfield, that often
“the term ‘rights’ tends to be used indiscriminately to cover what in a given case may be a privilege, a power, or an immunity, rather than a right in the strictest sense [a claims right] … [an] impression is conveyed that all legal relations can be comprehended under the conceptions, ‘right’ and ‘duty.’” 
Only a claims right imposes a duty on to a correlating party. NhRP agreed with the court that a legal personhood of a corporation, allowing it to exercise its claims right to contractual obligations, can be granted if and only if, it is capable of carrying out the duties of its contractual obligations. But, unlike this right to enter into a contract, immunity does not impose a duty on the correlating party. Instead, it is a recognition of the correlating party’s disability of control over the privileges and duties of the rights holder.
“The existence or nonexistence of Tommy’s ability to bear duties or responsibilities is entirely irrelevant, as it is irrelevant to every immunity-right [freedom of speech, freedom from slavery, right to an abortion…] It is particularly inappropriate to demand that, for Tommy to possess the fundamental immunity right to bodily liberty protected by the common law writ of habeas corpus, he must possess the ability to bear duties and responsibilities, when this ability has nothing whatsoever to do with his fundamental immunity-right to bodily liberty.” 
Taking a step back, it should be noted that in its decision the court addressed “the novel question of whether a chimpanzee is a ‘person’ entitled to the rights and protections afforded by the writ of habeas corpus.”  The right to file for a writ of habeas corpus is protected under the Constitution and defined in New York state as a right to both a petition for an inquiry into a cause of illegal detention as well as for subsequent “deliverance” from it. Under the Hohfieldian approach, aside from the right to liberty, this complex right also includes two other basic rights. The power to file the petition which correlates with the courts liability of being required to consider this petition. And, the requirement that the court use its power and guarantee the petitioner’s release if the petition is granted. If so, the government would have a duty to free the petitioner. This means that there is a duty correlating to one of the basic rights within the broader right to habeas corpus. Even if NhRP’s appeals argument is valid it would still fail because one of its premises turns out to be false.
So far there has been no decision on Tommy’s appeal. The two other cases are also ongoing but at earlier stages. You can follow the progress of these cases on the NhRP website.  There is a great New York Times article on the story behind this litigation and specifically Steven M. Wise, who is the founder and head counsel of NhRP .
PostScript, 21 April 2015: An order has just been issued on the writ of habeas corpus petition for Hercules and Leo, the two chimpanzees held at Stony Brook University. The order is titled “Order To Show Cause & Writ of Habeas Corpus” and it is all over the news as “the writ of habeas corpus has been granted!” However, The meaning of the order is that the petition has been accepted to be considered and it is now the respondents’ turn to argue why it should not be granted (and accepted in the first place). Just because, technically, the order is stating that the University has to show cause for Hercules and Leo’s detainment, it does not mean that they are now considered to be detained persons. The argument is still going to center on whether the petition should even be considered. In the previous cases the petitions never got to this stage.
Kirill Ershov is an attorney specializing in habeas corpus petitions contesting death penalty convictions. Primarily, the petitions are filed due to violations of an individual’s constitutional rights to a fair trial and to the effective assistance of counsel. He is licensed to practice in California and in federal court.
 Legal updates and all of the filings of these cases can be found here.
 Should a Chimp Be Able to Sue Its Owner? The NYT article has details on the background of the cases including the conditions of the chimpanzees.
 Tommy’s Petition’s Memorandum of Law.
 NY Code – Article 70: Habeas Corpus, Section 7002 – Petition.
 #3 starting at p. 39.
 #3 starting at p. 54.
 #3 at ps. 4 to 38.
 #3 at p. 61.
 #3 at p. 38.
 Tommy’s initial hearing transcript, at p. 12.
 Kiko’s initial hearing transcript, at p. 12.
 Kiko’s appellate hearing transcript, at p. 6.
 Kiko court of appeals decision, at p. 2.
 Tommy’s appellate hearing transcript, at p. 7.
 Tommy court of appeals decision, at ps. 3 to 6.
 Stanford Encyclopedia of Philosophy — Rights 2.1; Hohfeld, Wesley N., “Fundamental Legal Conceptions as Applied in Judicial Reasoning” (1917). Faculty Scholarship Series. Paper 4378.
 Tommy’s memorandum of appeal to the appellate court decision, at ps. 11 to 14.
 #17 at p. 12.
 #17 at p. 13.
 #15 at p. 2.
 The NhRP website.