# Chance versus Randomness

> 【EN】Randomness, as we ordinarily think of it, exists when some outcomes occur haphazardly, unpredictably, or by chance. These latter three notions are all distinct, but all have some kind of close connection to probability. Notoriously, there are many kinds of probability: subjective probabilities (‘degrees of belief’), evidential probabilities, and objective chances, to name a few (Hájek 2012), and we might enquire into the connections between randomness and any of these species of probability. In this entry, we focus on the potential connections between randomness and chance, or physical probability. The ordinary way that the word ‘random’ gets used is more or less interchangeable with ‘chancy’, which suggests this Commonplace Thesis—a useful claim to target in our discussion: (CT) Something is random iff it happens by chance. … 【中】日常所说的随机涉及偶然、不可预测与碰巧三种彼此有别的观念，都与概率相关；概率本身又有主观置信度、证据概率与客观机遇等多种类型。词条聚焦随机性与机遇的可能联系，讨论单称机遇与机遇过程、物理学中的机遇、马丁-洛夫式的能行随机性检验、前缀自由的柯尔莫哥洛夫复杂性、Schnorr 定理，以及共同论题的精炼、参考类问题与偏倚。

- ID: m13173
- Category: culture
- Domain: 哲学

## Definition

本词条考察随机性与客观机遇（物理概率）之间的关系。随机在日常理解中意味着结果的发生杂乱无章、不可预测或出于偶然，这三种说法彼此不同，却都与概率有某种密切联系。 脚手架作用：- 概念拆分：区分无规律、不可预测与出于偶然三种含义。 - 归因校准：判断该用客观概率，还是信息不足造成的表象。 - 模型选择：先检验序列是否真随机，再决定用哪种概率模型。

## How it works

随机性的形式刻画有两条路线：能行检验路线要求随机序列通过所有能行的统计检验；复杂性路线要求序列不可压缩。两条路线在满足前缀自由条件时重合。它们与机遇的联系则依赖共同论题：随机过程是机遇过程，随机结果具有非零的机遇。

## Practice

1) 先分清说的是主观不确定性还是客观机遇。2) 若指序列的随机，选用能行检验或不可压缩性标准，而不是凭看上去乱判断。3) 讨论机遇时明确参考类。4) 记住偏倚：小概率结果同样可以是随机的。

## Use

- 概念拆分：区分无规律、不可预测与出于偶然三种含义。 - 归因校准：判断该用客观概率，还是信息不足造成的表象。 - 模型选择：先检验序列是否真随机，再决定用哪种概率模型。

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