Learn Portuguese (Portugal): É provável que a tartaruga coma o plástico. - It's likely that the turtle eats the plastic.

The phrase É provável que (It is likely that) is an impersonal expression of probability. Whenever you express probability, doubt, or subjective opinions this way, it forces the next verb into the subjunctive mood. That is why the regular present tense come changes to the present subjunctive coma.

How is the subjunctive form coma made from the verb comer?

To make the present subjunctive for regular -er verbs, you swap their usual endings for -ar verb endings. You start with the 'eu' form of the present tense (como), drop the -o, and add -a for the a tartaruga (it/she) form.

Does É provável que always need to be followed by que?

Yes, when connecting this kind of impersonal expression to a new subject (like a tartaruga) and an action (coma), you must use the conjunction que (that). Unlike in English, where you can sometimes drop 'that', in Portuguese the que is absolutely mandatory.

Since the turtle hasn't eaten the plastic yet, why don't we use a future tense here?

In Portuguese, the present subjunctive is used after phrases like É provável que even when referring to something that might happen in the future. The present subjunctive itself often carries a future meaning because it describes an action that is hypothetical or hasn't actually happened yet.