Do I have a moral obligation to help someone who is being attacked?

No single philosopher provides a unanimous "yes" or "no" answer; their writings reveal a spectrum of views on moral obligation in this scenario (a bystander witnessing an attack on a stranger). The obligation—if it exists—is almost always qualified by considerations of risk to oneself, personal capacity, or character. Below is a focused synthesis drawn strictly from their key texts and theories.

Deontological / Duty-Based Views (Kant)

Immanuel Kant argues in Groundwork of the Metaphysics of Morals (1785) and The Metaphysics of Morals (1797, Doctrine of Virtue) that there is an imperfect duty of beneficence. You must adopt a maxim of helping others promote their own ends/happiness when it is within your power, because failing to do so could not be universalized under the categorical imperative (treating persons as ends, not mere means). Helping the attacked person would normally align with this duty—especially if low-cost or low-risk to you—because indifference to human suffering treats the victim as a mere means to your own convenience. However, it is imperfect: it allows latitude and does not require you to sacrifice your own rational ends or life. Kant grounds this in reason and autonomy, not emotion.

Natural Law and Preservation Duties (Locke)

John Locke, in Second Treatise of Government (1689, §6), explicitly states a positive duty under natural law and reason:

“when his own preservation comes not in competition, ought he, as much as he can, to preserve the rest of mankind.”

Every person, being God’s workmanship and equal, has a duty to aid in preserving others’ life and liberty when safe to do so. An attack on the street would trigger this obligation unless your own life is directly endangered. This is not optional charity but part of the law of nature that precedes civil society.

Virtue Ethics (Aristotle)

Aristotle, in Nicomachean Ethics (especially Books II–V and VIII on justice, courage, and friendship), does not frame the issue as a strict “rule-based obligation” but as the conduct of the virtuous person (phronimos). Justice is the complete virtue “in relation to another,” concerned with fairness and the good of others in the polis. Courage requires facing danger for the right reason. A person of excellent character would intervene (or summon help) as an expression of eudaimonia (flourishing) and justice—especially if the act is proportionate. Failure to act when one has the capacity would simply not be the action of a virtuous human being. It is character, not abstract duty, that binds you.

Compassion and Sympathy-Based Ethics (Rousseau, Schopenhauer, Hume)

• Jean-Jacques Rousseau (Discourse on the Origin of Inequality, 1755; Emile, 1762) identifies natural pitié (compassion) as a pre-rational sentiment that “carries us without reflection to the assistance of those we see suffer.” In the state of nature it precedes laws and is the true foundation of morality; civil society may corrupt it, but it still grounds an immediate, non-calculating impulse to help the attacked.
• Arthur Schopenhauer (On the Basis of Morality, 1840) insists that compassion (Mitleid) is the only genuine moral motive. Moral worth exists solely when you directly feel the other’s suffering as your own. Watching an attack would evoke this identification; helping is the only morally valuable response. Egoism or indifference has zero moral worth.
• David Hume (A Treatise of Human Nature, 1739–40; Enquiry Concerning the Principles of Morals, 1751) grounds morality in sympathy: we naturally approve benevolent actions that relieve suffering. Helping the victim would be the object of moral sentiment; failing to help (when easy) would provoke disapproval.

Utilitarian Calculus (Bentham and Mill)

Jeremy Bentham (Introduction to the Principles of Morals and Legislation, 1789) and John Stuart Mill (Utilitarianism, 1861) tie obligation to consequences: you have a duty to act so as to maximize overall happiness / minimize pain. If intervening (or calling for help) prevents greater harm than the cost or risk to you, you are morally obligated to do so. The duty is real but strictly conditional on the net utility calculation.

Skeptical or Qualifying Views

• Thomas Hobbes (Leviathan, 1651): In the state of nature there is no natural positive obligation to help; the fundamental right is self-preservation. Any duty arises only from the social contract and the sovereign’s laws. You may have a civil obligation if the state enforces it, but no inherent moral one that requires risking yourself.
• Friedrich Nietzsche (e.g., On the Genealogy of Morals, 1887; Thus Spoke Zarathustra) critiques “pity” and “duty to the weak” as symptoms of slave morality and Christian ressentiment that weaken the strong. True nobility may involve helping from overflowing power, but never from a binding “obligation.”
• Jean-Paul Sartre (Existentialism is a Humanism, 1946) and Emmanuel Levinas (20th-century French phenomenology, Totality and Infinity, 1961): Sartre denies any pre-given obligations—you are “condemned to be free” and must authentically choose whether helping defines your values. Levinas, by contrast, sees ethics as first philosophy: the “face” of the vulnerable Other places you under infinite, asymmetrical responsibility. The attacked person’s very vulnerability commands you prior to all ontology or self-interest.

Summary Across These Writings

Major traditions (Kantian duty, Lockean natural law, Aristotelian virtue, Rousseau/Schopenhauer/Hume compassion, and utilitarianism) generally affirm some form of obligation—perfect, imperfect, virtuous, or compassion-driven—especially when intervention is low-risk to you. Hobbesian, Nietzschean, and Sartrean perspectives treat it as conditional, absent, or freely chosen. There is no monolithic philosophical answer; the obligation (when it exists) is almost never absolute if it endangers your own life.