Should I use subjunctive in a sentence that is the consequence of another sentence that uses the subjunctive?

Question

For example, if I say "Supposons qu'il y ait [qch], cela signifie que ...", where "cela" refers to the "[qch]", then should I use the subjunctive of "signifier"?

Answer 1

You can use the conditional, not the subjunctive.

• Supposons qu'il y ait des erreurs, cela pourrait/puisse avoir de graves conséquences.

You can also use the indicative in the present.

• Supposons qu'il y ait des erreurs, cela peut avoir de graves conséquences.

Answer 2

No, you don't use the subjunctive for signifie.

"Cela signifie..." is a main clause. You could change the comma in your sentence for a full stop:

Supposons (main clause 1) qu'il y ait [qch] (subordinate clause). Cela signifie (main clause 2) que [...]

Most of the time, subjunctive occurs in a subordinate clause, not a main clause. You could however use conditional (cela signifierait que) to mark hypothesis.