The subjunctive mood in Spanish does not have an equivalent in Finnish. The subjunctive is used quite often in Spanish, though, which is why a native Finnish speaker studying Spanish has to struggle sometimes to assimilate the subjunctive if she or he wants to build a foundation for a good knowledge of Spanish.
Depending on the clause and context of the Spanish subjunctive, the equivalent mood in Finnish may be the indicative, the imperative or the conditional mood. As the subjunctive in Spanish expresses a wide variety of things and does not have a one clear determining feature that encompasses all of its uses, the only way for a Finnish speaker to learn to use the subjunctive mood in Spanish correctly is to learn each convention separately.
I will briefly illustrate this problem with few examples.
Example 1 – Adverbs of Probability (quizá/quizás): Subjunctive or Indicative Mood in Spanish, Indicative Mood in Finnish
In many cases, the equivalent of the Spanish subjunctive in Finnish is simply the indicative mood. The Spanish adverb quizá(s), which means maybe, is a bit tricky because a Finnish speaker has to contemplate the mood problem in Spanish first (subjunctive/indicative), which is confusing according to the conventions of Finnish, and then find an equivalent in Finnish.
The affected verb after quizá(s) (similar to tal vez and acaso) behaves differently depending on the level of uncertainty of the matter. Thus, quizá(s) per se does not indicate if the affected verb has to be in the subjunctive or indicative mood in Spanish. The Finnish equivalent is always in the indicative mood.
SP: Quizá algún día haya paz en el mundo. (EN: Maybe one day there will be world peace.)
FIN: Ehkä joku päivä maailmassa on rauha.
Low probability, unrealistic matter: Subjunctive mood (haya) in Spanish, indicative mood (on) in Finnish.
SP: Quizá viajo contigo. (EN: Maybe I will travel with you.)
FIN: Ehkä matkustan sinun kanssasi.
High probability, realistic matter: Indicative in both Spanish (viajo) and Finnish (matkustan).
Example 2 – Negative Commands: Subjunctive Mood in Spanish, Imperative Mood in Finnish
The negative forms of commands in Spanish act the same way as the present subjunctive forms. As the positive forms of commands have their own imperative verb forms, as they do in Finnish, the negative commands have to be studied as a special case. Naturally, they cannot be studied without some knowledge of the Spanish subjunctive mood and its conventions.
SP: ¡No le des azúcar a tu perro! (EN: Don’t give your dog sugar!)
FIN: Älä anna koirallesi sokeria!
Thus, Spanish uses the subjunctive mood (no des) and Finnish uses the imperative mood (Älä anna).
Example 3 – Relative Clauses, When the Correlate is Unknown: Subjunctive in Spanish, Conditional in Finnish
Spanish uses the subjunctive when the correlate of a relative clause is unknown (i.e., if it only exists in the speaker’s mind) or if the correlate has to fulfill certain requirements. Finnish resolves this “nonexistence” by using the conditional mood.
SP: Estoy buscando un bolso que haga juego con mis zapatos. (EN: I’m looking for a handbag that goes with my shoes.)
FIN: Etsin käsilaukkua, joka sopisi kenkiini.
In the example, Spanish uses the subjunctive mood (haga) and Finnish uses the conditional mood (sopisi).
Thus, a Finnish speaker will usually learn to use the subjunctive correctly in written Spanish but will keep making grammatical mistakes in spoken Spanish for a long time because a spontaneous speaking situation makes it a challenge to quickly recall the forms from memory. The Spanish subjunctive is not especially noteworthy for its abstruseness, but for the hard, and sometimes tiresome, memorization of each usage.