在伊斯兰教法根源学（Usul）中，某物被视为一种法源，是指它能够用来推导出新的律例（Ahkam）。类比推理（Qiyas）之所以是法源，是因为我们可以从中推导出新的律例。通过借助共同的“Illah”（致因）将原有的规定延伸到新的情况，便能得出适用于新情况的律例，因此类比推理是法源。这也是我们认识伊斯兰教适用于一切时代和一切地方的能力的途径之一，因为针对新的情况和问题，可以推导出相应的律例。

Something is defined as a source in Usul when it serves as a source for new Ahkam (rules). Qiyas is a source because we can extract new Ahkam from it. By extending the original rule to new realities via a shared „Illah, leads to new Ahkam for new realities and hence Qiyas is a source. This is one of the ways we can appreciate the capacity of Islam to apply to all times and places as Ahkam can be deduced for new realities and problems.

类比推理（Qiyas）总是建立在以下四个基本要素之上：

Qiyas is always built on the following four pillars:

i. 原则（旧有之事）。

i. Asl (old matter).

ii. 分支（新问题）。

ii. Fari‟ (new matter).

iii. 律例（Hukm）。

iii. Hukm (rule).

iv. "伊拉"（有效理由）。

iv. „Illah (effective reason).

例如，安拉（SWT）说：

For example Allah (swt) said:

“你们要为他们准备你们所能准备的一切力量和战马，以震慑Allah的敌人。”（TMQ《戒备》：60）

“And make ready against them all you can of power including horses to threaten the enemy of Allah.” (TMQ Al-Anfal: 60)

经文中给出的哈库姆（Hukm）是：备战是一项义务。旧有的事物是马匹。其伊莱（„Illah，即法定依据）是使真主的敌人感到恐惧。至于新出现的事物，则是任何能够实现备战之伊莱（即使敌人感到恐惧）的东西。因此，在当今时代，拥有坦克、战斗机和航空母舰也成为义务，因为它们能够使敌人感到恐惧。不仅如此，该伊莱还要求伊斯兰国在以下几个方面进行备战：

The Hukm given in the verse is that preparation is an obligation. The old matter is horses. The „Illah is to terrify the enemy of Allah. As for the new matter, it is anything that will realise the „Illah of the preparation, which is to terrify the enemy. So these days it would be obligatory to have tanks, fighter planes, and aircraft carries since they terrify the enemy. Not only that, the „Illah obliges the Islamic State prepare in the following areas:

a) 若要实现"震慑敌人"这一"illah"（动因），军工发展与战争工业就必须是其时代中最强大的。

a) The arms development and war industry must be the strongest of its age if it is to fulfill the „Illah of terrifying the enemy.

b) 国家不能依赖他人来获取其力量来源，因此它必须努力发展自己的武器和军备。

b) The state cannot depend on others for its sources of power and hence it has to strive to develop its own weapons and armaments.

c) 它应当拥有新式精良的武器，使敌人闻之胆寒。

c) It should have new sophisticated weapons which will strike fear in the hearts of the enemy.

根据伊斯兰教法根源学（Usul al-Fiqh）著作的阐述，类比推理（Qiyas）有其具体的准则与条件。其中一项准则是：对于所要类比的新情况，不应存在来自《古兰经》、圣训（Sunnah）以及圣门弟子的共识（Ijma‟ as-Sahabah）的现成裁决。

There are specific guidelines and requirements for Qiyas explained in the books of Usul al-Fiqh. One such guideline is that there should be no existing ruling from the Qur‟an, Sunnah and Ijma‟ as-Sahabah for the new case.

例：女性在做瓦都（小净）之前是否必须卸掉指甲油？有人声称女性在做瓦都时无需卸掉指甲油，他们以对擦脚套（马斯赫）的做法进行类比（قياس）来为此辩护。

Example: Does a woman have to remove the nail polish before performing Wudhu? Some people claim she does not have to remove the nail polish in order to do Wudhu, and they justify it by doing Qiyas on the performance of Masah (wiping over the socks).

由于关于礼拜前小净（Wudhu）的经文明确命令洗净双手的各个部位，而指甲油会阻止水到达指甲，因此在这种情况下不能进行类比推理（Qiyas）。至于隔着袜子擦拭（Masah），经文中并未给出其法律依据（'Illah），因此不能将其推广到其他事物上。所以，在这个问题上可以运用类比推理（Qiyas）。

Qiyas cannot be performed in this situation because the Ayah regarding Wudhu explicitly orders to wash all parts of the hands, and polish prevents water from reaching the nails. In the case of Masah (wiping over the socks) the text is not presented with an „Illah (legal reason) and cannot be extended to other things. Thus, Qiyas can be practiced in this issue.

除此之外，卡亚斯（类比推理）的其他条件还包括：原始的判决必须来自《古兰经》、圣训和圣门弟子的一致意见（伊吉玛尔·萨哈巴），而不能来自另一个卡亚斯；并且《古兰经》、圣训和圣门弟子的一致意见的经文中，必须包含该判决的理由。我们不能运用我们的理智（阿格勒）去推导出判决的起因（伊莱）。

Some of the other requirements for Qiyas are that the original ruling has to be from Qur‟an, Sunnah and Ijma‟ as-Sahabah, not from another Qiyas. In addition, the texts of the Qur‟an, Sunnah and Ijma‟ as-Sahabah must contain the justification for the ruling. We cannot use our „Aql (intellect) to come up with the cause („Illah).