Comprendre vs. saisir

The French words 'comprendre' and 'saisir' can both translate to 'understand' or 'comprehend' in English, but they are used differently and convey slightly different nuances of understanding.

Comprendre

'Comprendre' refers to the ability to grasp the meaning or the concept of something. It implies a deeper level of understanding, often regarding intellectual or complex ideas.
Je comprends la théorie de la relativité.
(I understand the theory of relativity.)
Il est important de comprendre les instructions avant de commencer.
(It's important to understand the instructions before starting.)
Elle comprend vite quand il s'agit de mathématiques.
(She understands quickly when it comes to mathematics.)

Saisir

'Saisir' also means to grasp or comprehend but is often used in more immediate or basic contexts. It might imply a quicker, sometimes physical, grasp or catching on to something.
Saisis-tu l'ironie de la situation ?
(Do you grasp the irony of the situation?)
Il a saisi l'idée après une courte explication.
(He caught on to the idea after a short explanation.)
Saisissez cette opportunité avant qu'il ne soit trop tard.
(Grasp this opportunity before it's too late.)

Summary

'Comprendre' is typically used for a deeper or more abstract level of understanding and is akin to a thorough comprehension of a subject. In contrast, 'saisir' often relates to a quicker, sometimes less profound grasp of information or situations, closer to 'catching on' or 'grasping' an idea more immediately.