MIT theoretical linguist Shigeru Miyagawa’s cross-linguistic and historical inquiry into direct objects

His point is quite interesting.

In modern English, a direct object is marked by word order, and the order is fixed. In modern Japanese, it is marked by case marking, and its word order is not fixed.

But to go back in history gets you to understand that the situation was opposite. That is, old Japanese marked direct objects by word order, and old English marked them by case marking as Latin did.

Ways of making direct objects are strictly restricted: there are only two ways. And it seems that all languages select the way from two.

Saussure noted that languages can vary arbitrarily, but at least some modern linguists think opposite.