What are the differences between Japanese and western-style kitchen knives?


Kitchen knives are generally classified into two categories: Japanese and Western-style ones. Japanese kitchen knives are further classified into two: single-bevel knives and double-bevel knives. Today,  we'll focus on double-bevel knives and compare it with western kitchen knives. Let's save the topic on single versus double bevel knives in a different article.

STEEL: soft versus hard

Western-style knives are typically made of steels such as  X50CrMoV15 (e.g. Wusthof, Zwilling) or 440C (e.g. Cutco). These steels have a hardness of around 55HRC. The famous Wüsth of classic chef's knife has a hardness of 56HRC. On the other hand, Japanese kitchen knives are made of steels like Hitachi shirogami#2 or Takefu VG10 with hardness of at least 60HRC. The most recommended starter gyuto, Tojiro VG10 has a hardness of 61HRC. High-end Japanese steel like AS or SG2 can be up to 64HRC.

As you can see, one of the general differences between these knives is that Western-style ones have softer steel while Japanese have harder steel. Western-style ones are more robust but they don't have the excellent cutting ability and  edge retention of Japanese kitchen knives.

 

If you value edge retention and outstanding cutting performance, get a Japanese kitchen knife. If you just want an all-arounder that can take some abuse (but requires frequent sharpening), the Western-style knife is better. Knowing your preferences will allow you to make the correct decision.
Japanese = hard = delicate edge = excellent edge retention =
Western = soft  = tough and robust edge  = low edge retention = more frequent sharpening

THICKNESS and WEIGHT: thick/heavy versus thin/light

Japanese kitchen knives are much thinner and are thus much lighter compared to their Western counterparts.
In general, the thinner the knife is, the better it is at various cutting tasks. This difference in cutting performance is more obvious when you handle dense vegetables like carrots. Try using a Japanese kitchen knife like a gyuto and it will easily cut through a carrot. In contrast, cutting such vegetables with a Western-style chef's knife would require more force. This is because of the Western-style knife's relatively thick cross-section from the spine and down at the edge.
In reality, one is not better than the other as it depends on the task at hand. For general cutting tasks and fine work, a Japanese kitchen knife is better.  For heavier work, the Western-style knife should be your go-to. This is why most professional chefs as well as home cooks have two general-purpose knives: one Japanese multipurpose knife like a gyuto for precision cutting tasks and one Western-style knife (a "beater knife") for rough  tasks.

TANG: full versus partial

Japanese kitchen knives with wooden handles have partial tangs. This contributes to the knife's excellent balance and lightness making them excel at agility and ease of manipulation for fine work.
Western-style knives have full tang resulting to a more handle-heavy balance. There are also Japanese kitchen knives that have a full-tang construction but with a slightly different balance (more blade-forward) because of their thinner and lighter blades.
Note that tang construction is  based on practical utilitarian reasons and does not reflect a knife's overall quality.  We're saying this because there's a misconception going around that full tangs are the "best" and are even used as marketing phrases to attract customers implying that it has "superior quality". Of course, this is incorrect.
The rationale for full tang is that it allows for increased force and leverage. For survival knives or heavy-duty knives like bone choppers, full tang construction makes sense. You indeed need some force to do some heavy-duty tasks and having a full tang would be beneficial. 
On the other hand, for kitchen knives where you only use it to cut vegetables or (boneless) meat, tang construction does not really matter. Tang construction should not be a major factor when you're making a decision. Either type is fine and the best one depends on your preferences.