Beyond locutionary and illocutionary acts, perlocution describes effects achieved by performing a speech act: persuading, frightening, or convincing. Perlocutionary success depends on causal consequences, not conventional meaning. Distinguishing perlocution from illocution clarifies when communication succeeds or fails at different levels and why intent alone doesn't guarantee communicative success.
Austin's analysis of speech acts distinguished three levels of action in any utterance. From your study of speech acts, you know the locutionary act — producing meaningful sounds or marks — and the illocutionary act — the conventional force of the utterance (asserting, promising, ordering, warning). The perlocutionary act is the third level: the *effect* produced in the hearer by performing the illocutionary act. Where illocution is about what you do with words by convention, perlocution is about what you causally bring about in the world through words.
The examples are intuitive once you see the structure. The illocutionary act of *warning* can have the perlocutionary effect of *alarming* the listener — or it might not, if the listener doesn't believe the warning or doesn't care. The illocutionary act of *arguing* can have the perlocutionary effect of *convincing* — or the listener might remain unpersuaded. The illocutionary act of *insulting* can have the perlocutionary effect of *humiliating* — or the target might shrug it off. The same illocutionary act can yield different perlocutionary outcomes depending on the hearer's background beliefs, emotional states, and choices.
This asymmetry marks the fundamental difference between illocution and perlocution. Illocutionary success is governed by conventions and uptake: a promise succeeds if the speaker utters the right words in the right context and the hearer understands that a promise has been made. Perlocutionary success is governed by causal consequences and cannot be guaranteed by any conventional formula. You can perform the illocutionary act of promising perfectly and still fail to reassure your audience. You can give a technically valid argument and still fail to persuade. The causal chain from speech to mental effect runs through the hearer's psychology in ways the speaker cannot fully control.
This distinction has significant implications. In rhetoric and persuasion theory, the question is what causal mechanisms connect speech acts to belief change, emotional response, or action — a question that depends on psychology and audience characteristics, not just linguistics. In philosophy of action, it clarifies why we do not normally hold speakers fully responsible for perlocutionary effects in the way we hold them responsible for illocutionary acts: I can be blamed for promising when I had no intention of keeping my promise (the illocutionary act), but whether my reassurance *caused* you to feel reassured depends on factors I don't control. In legal and ethical contexts, the distinction matters for questions about harassment, defamation, and incitement — where the harm is often perlocutionary but legal liability typically requires identifying the illocutionary act performed.
One further subtlety: perlocutionary effects can be intended or unintended. A speaker who sets out to persuade intends the perlocutionary effect of belief change; a speaker who inadvertently frightens a listener with an offhand comment produced a perlocutionary effect they did not intend. Austin noted that some perlocutionary effects can be "aimed at" and others merely "brought about" — a distinction that begins to draw a line between strategic and merely causal influence through language, which becomes central in downstream work on performativity and the ethics of rhetoric.
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