Once in a while, grammar matters, and the title of “The Other Son” is an example. It doesn’t tell you much about this drama, in which 18-year-old Jewish and Palestinian boys find out they were switched as infants.

But the French title translates as “The Son of the Other.” Now we know where we are – in a country where the people unlike us are “the other,” something to be segregated or despised or feared.

So it goes with the families of Joseph (Jules Sitruk) and Yacine (Mehdi Dehbi). They were born during the Gulf War of 1991, when a SCUD missile hit their hospital and forced an evacuation. When Joseph signs up for Israel’s obligatory military service and learns his blood type differs from both parents – a genetic impossibility – detective work reveals the mistake.

The story creates conflicts on a basic level. Alon, Joseph’s dad (Pascal Elbé), works in Israel’s Ministry of Defense. Said (Khalifa Natour), Yacine’s father, lives in humbler circumstances in a Palestinian settlement on the West Bank; he’s trained as an engineer but forbidden to practice outside his home town, so he repairs cars.

Neither man can speak civilly to the other for 30 seconds.

Yet director Lorraine Levy, who wrote the script with Nathalie Saugeon, is more interested in non-political identities. Yacine’s brother (Mahmood Shalabi) renounces him as a newfound Jewish “oppressor.” A rabbi informs Joseph that, although the boy has been bar mitzvahed and spent his entire life attending a synagogue, he’s not a Jew, because his mother was not Jewish at the time of his birth.

The mothers, Orith and Leila (Emmanuelle Devos and Areen Omari), see the sensible course: Keep loving the sons they’ve known all their lives and make room in their hearts for the boys they have yet to know. “You are my third child,” Orith tells Yacine, referring to Joseph and her little daughter. In fact, all the females ignore the nature-nurture debate: Yacine and Joseph’s little sisters immediately become friends.

The filmmakers must have been tempted toward melodrama many times: Yacine stopping a suicide bomber, say, or Joseph saving his new Palestinian family from Israeli soldiers. They resist this temptation, except for one brief, violent incident that comes out of nowhere and doesn’t fit in naturally.

The movie doesn’t need to preach a “we’re all equal” message. When we watch the boys bond with their new kin over food or music, then see the lines of Palestinians plodding through armed checkpoints to reach jobs or visit Israeli friends, we get the point: These two Semitic peoples are bound by traditions and genetics but divided by seemingly irresolvable politics.