Apparently gésir has an incomplete conjugation—it only works in the present tense. This confuses me. How would I say “I would lie down” or “I will lie down”, etc?
Gésir implies more than just lying down; the subject has to be incapacitated and not be able to move. It's mainly used on dead people's graves, where ci-gît stands for "here lies ..."
You can find all the common conjugations of gésir at le conjugueur. You have imparfait and present participle, too. As to I would lie down and its mates, I would use je serais couché, as in [se coucher].
Or you could innovate. Try j'aurais gési, je giserais…
How to translate “I would lie down” or “I will lie down”?
The usual translations for “lying down” are “être couché” or “être allongé”.
As was previously said, “gésir” implies the subject is incapacitated. It is common to see it in epitaphs in the form “Ci-gît …”, meaning “Here lies …”
Définition : Être étendu, couché, sans pouvoir se mouvoir (par suite d'un malaise, d'une blessure, d'une maladie, ou de la mort). Être couché dans la tombe, être enterré.
Conjugaison : Gésir est un verbe défectif que l'on rencontre surtout au présent (je gis, tu gis, il gît, nous gisons, vous gisez, ils gisent), à l'imparfait (je gisais, etc.) et au participe présent (gisant, gisante). L’infinitif est encore employé.
Exemple : Vous semblez gésir côte à côté. (Georges Bernanos, Mauvais rêve, 1948)
Why is “gésir” defective?
Because of their meaning, many verbs in French cannot be conjugated at all persons or tenses.
For example, French's passé simple is used to describe an action taking place at a specific moment in time. Imparfait is used for descriptions and actions occurring over a span of time. Both tenses are past simple in English. Thus, some verbs cannot be used with passé simple because they describe something which is not instantaneous or for which the time of occurring cannot be precisely defined.
Other defective verbs are just remnants from the past, used only in specific forms or expressions (“issir” is only used as a past participe “issu”). Accounting for those is difficult.
If you want some analogy with English, “to be born” can only be used in passive voice because the subject can only be the receiver of the action.
Answer built upon the exchange with GAM PUB
Defective verbs are common in French, for example, a simple verb such as DISTRAIRE (‘to entertain’) has no simple past (French speakers don't know the forms), CLORE (‘to close’) is not used in present indicative 1pl and 2pl (even though, everyone knows the forms would be closons and closez).
In the case of GESIR, actually the infinitive you mentionned to designate the verb, is never used besides being the name of this verb.
I am french and I am 26. I just realized that "gésir" can't be used with passé simple or futur. I am pretty surprised about this. I always assumed that it was simply :
(passé simple) gisas, gisas,gisa,gîsâmes,gîsates,gisèrent (futur) Gésirai, gésiras, gésira, gésirons, gésirez, gésiront
I always used them in normal conversations. it never have been an issue in any way. I understund it and I was understooden. To me, they don't even sound weird.
Actually, I ended here because I wrote it on my laptop and that it told me that it was a mistake. I checked and I realized the terrible truth ! Then I look for the reason and this website is the first one I found with an explanation why it is this way. All french websites I checked just casually only give présent and imparfait with no explanation. Like if it was absolutly obvious.
Conclusion : Yes, Gésir officially doesn't exist in Futur or Passé simple. However, if you're not talking/writing for an exam, you can just do it. I would say that only French teachers will know that what you say is technically uncorrect even if perfectly understandable.