Despite the very frequent use of these different forms, some are incorrect. ils croivent/ils croient, que je voie/que je vois/que je voye. What do you think are the correct forms?
The amalgam between these different forms is very common in the oral use of the language. Listen around you and you will hear these mistakes in French.
ils croivent / ils croient
In oral it is very common to hear ils croivent. This conjugation of the verb croire is however false, it does not correspond to any time in the French language.
It's a mistake that a French teacher or an automatic proofreader would not let through. And this is confirmed by theAcadémie française (croivent/croient), ils croivent is not authorised.
So we have to say ils croient
que je voie / que je vois / que je voye
Similarly for the verb voir, despite a deep-rooted habit that goes back a long way, to say I must see, this form is false and must be corrected by I must see
This is valid for the singular, and the third person plural of the subjunctive.
You have to say : que je voie, que tu voies, qu’il voie, que nous voyions, que vous voyiez, qu’ils voient
And no : que je voye, que tu voyes, qu’il voye, qu’ils voyent
Do not confuse the present subjunctive (présent du subjonctif) with the present tense (présent de l’indicatif) where the "e" are replaced by "s"
These errors were parodied
The newspaper Le Gorafi even made a parody in 2014:
The French Academy finally validates "Ils croivent" and "Faut qu’on voye"