THE first and only televised debate between Angela Merkel and Martin Schulz, her Social Democrat (SPD) challenger, takes place tonight from 20:15 local time. This is his best chance to draw the chancellor into combat. Until now she has declined to engage with his criticisms, barely even mentioning his name. Along with others Mr Schulz accuses Mrs Merkel of “asymmetric demobilisation”: strategic inoffensiveness designed to lower turnout among the prospective supporters of rival parties, especially his own.

There is at least a little truth to the accusation: the chancellor's essential political weapon is her detachment. This is partly a question of tactics (like ignoring his points) as well as bearing (the chancellor’s voice is soothing, even soporific, and her body language calm and controlled). But most of all it is a function of her rhetoric. When justifying a divisive move or discussing a sensitive topic Mrs Merkel typically obscures differences, keeps her options open and denies her opponents new attack lines.

She does this by keeping her language in the politically propitious grey zone between responsive pertinence and stonewalling obstinacy. She may not always fully answer questions, but she does not entirely not answer them either. Her words are to her meaning what a thick blanket is to a piece of furniture: you can make out the rough shape, but not always identify what it is. All of which is the function of her toolbox of rhetorical devices:

Suggestive apposition. This involves making two adjacent or near-adjacent points implying, but not confirming, that there is a direct relationship between the two. The best example is Mrs Merkel's now famous speech in Trudering (a district of Munich) in May: “The times when we could entirely rely on others are somewhat over. I’ve experienced that in the past few days. And so I can only say: we Europeans must take our fate into our own hands; of course in friendship with America, in friendship with Britain…”. You have to admire the craftsmanship: in a couple of sentences the chancellor distanced herself from Donald Trump without saying anything remotely inflammatory. Also characteristic of Mrs Merkel was her implicit denial of alternatives: “so I can only say”.

Vaporous pronouns. Mrs Merkel has a knack for using “we” and “one” to obscure the subject of a sentence, and words like “it”, “this” and “that” to be vague about the object. Take her entreaty to Germans during the refugee crisis: “Wir schaffen das” (meaning “We’ll manage it” or “We can do it”). Who precisely was the “we” there? The chancellery? The federal government? The German people? Was she saying that the government could master the situation—or that it could not, so needed the governed to roll up their sleeves? And what was the “that” that this vague “we” would be managing? Such vagueness arises particularly on contentious topics: “Indeed, then one also leaves no-one behind” Mrs Merkel once said in defence of a domestically unpopular Greek bailout. The “one” and the “no-one” here were capacious enough to encompass all manner of meanings.

Qualifiers and mollifiers. The chancellor stuffs sentences with words that detach her somewhat from the meaning. Take the Trudering speech. She did not say “The times when we could rely on others are over” (which would have been a fair claim, Mr Trump being obviously unreliable) but “The times in which we could entirely rely on others are somewhat over.” Other phrases in this genre are “in the direction of”, “to some extent”, “in this context”, “on this subject”, “something like”. Probably Mrs Merkel’s pièce de résistance was her response in June to an unanticipated question about her opposition to equal marriage. Having ramblingly recalled a meeting with a lesbian couple in her constituency the chancellor concluded: “And therefore I would like to lead the discussion more towards a situation in which it is somewhat in the direction of a question of conscience”. This was, it later transpired, effectively the announcement of a historic Bundestag vote on equal marriage.

Compound adjectives. Words in German are like bricks: you can stack them up to achieve brilliantly precise terms like Torschlusspanik (gate-shut-panic, or the fear of running out of time to seize an opportunity). But such constructions can serve imprecision, too. Mrs Merkel has a habit of using compound adjectives (noun-adjective words) when more committal, less wooly alternatives would do. Her methods are not effective but “results oriented” (ergebnisorientiert) or “achievement capable” (leistungsfähig). Her policies are not tough or durable but “future capable” (zukunftsfähig).

Hollow intensifiers. All this vagueness runs the risk of Mrs Merkel’s language seeming too bloodless. Here intensifiers like “so”, “very”, “extremely” and “really” help; often deployed before a turn in her argument like “but”, “although” or “nonetheless”. They provide a patina of urgency and directness.

Hyper-generalisms. The above might make it sound like Mrs Merkel’s sentences are all unending and impenetrable. They are not. Like all good politicians, she can turn out short, sharp, sloganistic phrases. It is just that hers are particularly weightless. Take this quote from an interview in 2015: ”Germany is a strong country. Germany is a great country. I like my country. But it's not just me. Millions of others like this country.” Try disagreeing with that. At a “future dialogue” in Berlin she once circuitously theorised: “Everything that hasn’t yet existed is the future—if it does not yet exist”. Or consider this from a speech last October: “Last year was a very challenging year. So was this year. But different from how it was last year. I can give you the nice future prospect of a next year that will also be a very special year. So don't think it will be easier. But it will always be different.”

Irreverence. Mrs Merkel does a nice line in mild mockery. At her summer press conference last week, for example, she was indignantly asked why she only gives such audiences once a year. “How often would you like me to attend?” she enquired, straight faced. She deploys similar putdowns in dealing with macho pugilists on the world stage. “I understand why he has to do this—to prove he’s a man”, she observed dryly after one chest-puffing display from Vladimir Putin.

Acclaim, don't attack. The political scientist William Benoit says there are three modes of political communication: acclaim (present one’s record and proposals without comment on one’s rival), attack (criticise one’s rival) and defend (preempt or rebut criticisms of one’s self). Researchers at Hohenheim University studied the TV debate in 2013, pictured above, and found that Mrs Merkel spent 1326 seconds of her allocated time acclaiming, while Peer Steinbrück (her SPD challenger) spent 873 seconds doing so; she spent 112 seconds attacking, he spent 433 seconds on it. The two spent a similar amount of time on defence.

Where do these techniques come from? Some observers root them in Mrs Merkel’s upbringing in East Germany, where verbal ambiguity and passivity could keep one out of trouble. Yet her rhetorical style is not noticeably shared by other older “Ossis” in German politics (say, Joachim Gauck, Germany’s former president, or Stanislaw Tillich, the minister president of Saxony).

More convincing is the claim that it is the product of necessity. Mrs Merkel has never been a great public speaker—she began her political career as a somewhat awkward spokeswoman for the pre-unification East German government—but over the years has made a virtue of this by honing a cautious, detached and unvarnished speaking style that offends few and, to many, conveys unspun authenticity. It is like a suit of armour worn by a weak boxer: it makes her even less agile than she already is, but invulnerable enough that this (probably) does not matter.

Can Mr Schulz find the weak points? I have now witnessed him and Mrs Merkel each speak at several campaign events and can confirm that he is the better public speaker. He varies his rhythm, pace and volume to good effect; he speaks more emotionally and evocatively but can also be more concrete than the chancellor. To date, however, this skill has done him little good. Mr Schulz is far behind Mrs Merkel in polls of both party support (today’s Emnid survey puts her CDU/CSU on 38% and the SPD on 24%) and personal approval. If he cannot put the deftly evasive chancellor on the spot tonight, he probably never will.