The quotation from Mr Renan is displayed at a fascinating exhibition at the Petit Palais in Paris, which chronicles the artistic and political relationship of two peoples in the 19th century: a relationship of mingled fascination and terror; loathing and admiration.
The objects on display include the Emperor Napoleon's personal campaign map of the German states, village by village, at the close of the 18th century (when he was hailed as a democratic saviour before being turned out as an oppressor); a copy of the pacifist leaflet dropped unavailingly on Prussian troops from a balloon in 1871 by the novelist Victor Hugo (a very popular author in Germany); and a beatific painting of the German composer Richard Wagner by the French impressionist painter Pierre-Auguste Renoir, painted when the francophile Wagner had become viscerally anti- French, without seriously damaging the popularity of his music in France.
The exhibition - Un Siecle de Passions Franco-Allemandes (a century of Franco-German passions), previously shown in Berlin - goes on until 15 February. It coincides with 35th anniversary of the signing of the Elysee treaty by De Gaulle and Adenauer, a treaty which officially laid Franco- German enmity to rest. France and Germany are now the closest political and diplomatic couple in the world. Or are they?
The treaty, signed at the Elysee Palace in January 1963, spoke of a "profound change in the relationship between the two peoples". Three-and-half decades on, the diplomatic-economic partnership between the two is the core of the European Union. It has grown into the skin, and the bone, of the domestic politics of the two countries: something no mainstream politician in either country would dare to challenge (until recently). The creation of the euro is many things, but, politically, it is first and foremost a marriage between the deutschmark and the franc.
Remember that extraordinary picture of Chancellor Kohl and President Mitterrand hand in hand at Verdun. Consider the Franco-German military brigade, commanded alternately by French and German officers, which paraded on the Champs Elysees in 1994. In Strasbourg last year, I myself witnessed, the startling sight of young French and German anarchists fighting side by side against French riot police (supposedly to protest against the National Front).
And yet, in the broader sense, there is no new "relationship" between the French and German peoples to match the strength of the relationship between governments and political elites. It is a partnership of the national brains, but not truly of heart or bodies. "French and Germans, 35 years on," wrote the magazine Le Point, "are like neighbours on the same landing who have only a nodding acquaintance with one another."
The old visceral enmity is largely gone; 63 per cent of French people have a generally "good impression" of Germany. But lazy prejudices and generalisations colour the view, both ways, across the Rhine. The French see the Germans as disciplined, predictable, hard-working and humourless. The Germans see the French as charming, witty, superficial, arrogant, lazy and unreliable.
In the 19th century - and up to the middle of this century - the French and Germans fought and hated each other but remained fascinated by the culture of the other. Since the 1960s, the two countries, or at least the two governments, have worked intimately together, but the two peoples have increasingly lost interest in each other.
Does this matter? Perhaps not directly, until now. There are signs that the political marriage between the two countries is moving into a new and less stable phase. The glue of a broader, more popular friendship between the countries might have been useful to cement the future relationship between Paris and Berlin, which will inevitably be different from the relationship between Paris and Bonn.
The collapse of the Soviet bloc has re-united Germany and shifted German political and economic attention to the east. The fact that it is 53 years since French and Germans fought each other has diminished the emotional- symbolic importance of the relationship to a younger generation of politicians. There are unquantifiable psychological changes in both countries: a resurgence of German confidence and self-absorption; a diminution of French self- assurance.
The anniversary of the Elysee treaty has been marked by no particular state events. There were quarrelsome exchanges at a Franco-German parliamentary conference last week. The French minister for Europe, Pierre Moscovici, has written about "strong differences of interest" between France and Germany. At the Amsterdam and Luxembourg European summits last year, there was no pre-cooked Franco-German position on the main business of the day (something unprecedented in recent years).
Monetary Union, if it fails, provides endless and destructive opportunities for Franco-German recrimination. The chances are that it will not fail: France and Germany, and the others, have too much riding on the project domestically. But even harder tests are to come. In the next chapters of the EU agenda - enlargement to the east, farm policy and budgetary reform, the remodelling of EU institutions - French and German policies, and interests, suddenly seem diametrically opposed.
There has been a shifting of ground, almost a changing of sides. Germany, once so keen on federalism, wants a rapid enlargement to a modest number of eastern countries. But Bonn is playing down the need to give more power to Brussels to manage this sprawling new EU. It is also warning that it will not hand over many more German euros to the EU budget to make enlargement possible.
It is France, traditionally ambivalent about federalism, which is pushing for greater institutional reform, and strengthening, in Brussels and a much slower and wider enlargement. (The underlying French fear is that the German approach could destroy the EU farm policy and European subsidies to the French regions and make France a huge net contributor to Brussels for the first time).
Whoever wins the German election in September, the potential for Franco- German discord is enormous. A perfect opportunity for Blairist Britain to move to the centre of European policy-making? Maybe. Gerhard Schroeder, who could be the SPD Chancellor-candidate in September, spoke this week about replacing the German-French axis with a German-French-British triangle. Such comments have been heard before, in Paris as well as Bonn, without much coming of them. In any case, a triangular relationship would still require France and Germany to agree. It would be in no one's interest - certainly not Britain's - for an orderly enlargement and reform of the EU in the next decade to founder on Franco-German quarrels.
Another case of a misunderstanding which can only get worse?