“猜”、“猜测”、“猜想”这三个动词都表示推测。“猜”在口语中最常用，不能做主语、宾语，不能受定语修饰。“猜测”可做主语、宾语。“猜想”除了推测的意思，还表示估计、想象，可作呼吁、宾语，并可以用于科学推测命题。
The three verbs 猜，猜测 and 猜想 all mean "conjecture". 猜 is mostly used in colloquial language. It cannot function as the subject or object and cannot be qualified by an attributive. 猜测 functions as the subject and object. 猜想, besides the meaning of "guess", also means “estimation" and can function as the subject and object. It can also be used as the topic of scientific conjecture.
“猜谜”、“猜谜语”、“猜灯谜”，只能用猜。以下生活用语，也常用猜。
To guess a riddle, only 猜 can be used. In the following everyday speech，猜 is usually used.
（1）你猜我是谁？
（2）你猜猜这条鱼多少钱？

在较正式的说法中，三个词可以互换。
In more formal expressions, the three words are interchangeable.
（3）我猜（猜想/猜测）这件事一定会上报纸的头版。
（4）人们都在猜（猜想/猜测）他们之间的关系。

但“猜测”、“猜想”可作主语、宾语，可受定语修饰。
猜测 and 猜想 however, can function as the subject and object and can be qualified by an attributive.
（5）这种猜测（猜想）是没有根据的。
（6）这仅仅是一种猜测（猜想）而已。
（7）在调查之前我们可以大胆地去猜想（猜测）。
“猜测”还可以做定语，如“猜测之词”。
猜测 can also function as an attributive, as in 猜测之词。