The words “Lest We Forget” are spoken on Remembrance Day, commemorating the end of the First World War when the armistice brought hostilities to an end “at the 11th hour of the 11th day of the 11th month.” Remembrance services often conclude with the ‘Ode to Rembrance,’ a stanza from Laurence Binyon’s For the Fallen (which, written as early as 1914, presages the tenor the war would take over the years):
They shall grow not old, as we that are left grow old:
Age shall not weary them, nor the years condemn.
At the going down of the sun and in the morning
We will remember them.
“Lest we forget,” while carrying an almost imperative meaning of “it should not be forgotten,” means “in order that we not forget,” perhaps with a shade of the the other sense of lest expressing fear that we will indeed forget. Lest is among the few English conjunctions that require a subjunctive, or, often serving just as well, a should+ infinitive construction. In English, the present subjunctive is largely indistinguishable from the ordinary indicative mood since its form in most contexts is identical. Only in the third person singular does it differ in not having the –s ending of the present indicative (he face rather than he faces) and in the verb to be (I were rather than I was, and they be rather than they are).
OED gives two uses of lest:
1) A negative particle of intention or purpose, introducing a clause expressing something to be prevented or guarded against: in order that…not.
2) After verbs of fearing or phrases indicating apprehension or danger, introducing a clause expressing the event that is feared.
For example, 1) He kept his notes by his side lest faulty memory lead him astray; and 2) Let me try to make clear what I do not mean to be claiming in this section, lest I be taken to be arguing for more than I intend to be. (In either of these sentences the “bare infinitive” of the 3rd person present subjunctive” can be replaced by “should + infinitive”, e.g. … lest faulty memory should lead …) Another example of 2) from the academic corpus: Theorists should be cautious lest they consider a single cognitive process, such as anchoring, without giving equal weight to an opposing counter-process. And of 1) from Jane Austen:
The arrival, therefore, of a sister whom she had always loved, and now hoped to retain with her as long as she remained single, was highly agreeable; and her chief anxiety was lest Mansfield should not satisfy the habits of a young woman who had been mostly used to London.
Even if the clause preceding the clause introduced by lest is in the past, the present subjunctive is used in the lest clause – as in He kept his notes by his side lest faulty memory lead him astray. For this reason, some prefer to classify the present subjunctive here as an untensed bare infinitive carrying its own modality, preventing any change of tense to match that of the main clause and obviating the need to add any modal verb such as should.
The present indicative modal may is put into subjunctive form might: I was afraid lest someone might hear. However, inclusion of a modal such as might, would, could or should is often redundant to the modality borne by lest vis-a-vis a feared future outcome, and just the bare infinitive of the present subjunctive need remain: I was afraid lest someone hear. Expressing purely in the subjunctive present this way conveys perhaps more strongly the expectation that the fear eventuality will indeed occur, rather than it being a subjective fear that might not happen. Likewise, the use of should + infinitive conveys perhaps more the futurity of the feared outcome rather than its more immediate occurrence expressed by the futural present suggested by the present subjunctive form: … her chief anxiety was lest Mansfield not satisfy… still conveys the feared dissatisfaction on the part of the sister, only the fact that is a fear of a future development is not as well conveyed as by … should not satisfy …
In Visser’s ‘An Historical Syntax of the English Language’ examples from the last half-millennium are given of the lest + bare infinitive construction (image courtesy a contributor to an English Stack Exchange post on lest) :
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