92 A SPANISH REFERENCE GRAMMAR

alla, I must go there. Weakest of all would be he de ir alla, I am to go there. 425.

i6. When any tense of deber is followed by the perfect infinitive, the obligation is expressed as existing in the time of the tense of deber that is used, but the action or state expressed by the dependent infinitive is represented as prior to that of deber: debo ir

I ought (now) to go there; debo haber ido alla, I ought (now) to have gone there (before); debi ir alla, I ought (at that time) to have gone there (at that time); debi haber ido alla, I ought (at that time) to have gone there (before). 426.

17. Deber de + infinitive expresses probability, likelihood or inference, debe de ser rico, he must be, probably is, rich. Equivalents would be the future or potential of probability (see 493, 522, 652, 653) of the dependent verb, or haber de + infinitive: sera rico, ha de ser rico. 427.

For the use of debiera in expressing in a mild manner an obligation, see 571.

i8. When any tense of deber de is followed by the perfect infinitive, there is expressed the probability that the action of the infinitive occurred prior to the time of the tense of deber de : debe de ir alla, he must be going there (now); debe de haber ido he must have gone there, it must be (now) that he has (previ-

QUE AS CONNECTIVE   93

ously) gone there; debi6 de ir alla, he must (at that time) have been going there (at that time); debi6 de haber ido he must (at that time) have gone there (before). 428.

19. The infinitive is connected by de with a verb of cessation upon which it depends: dej6 de hablar, he stopped speaking; cesii de mirarme, he ceased looking at me; acabli de hacerlo, he finished doing it. 429.

zo. Other prepositions used as connectives before infinitives are en (after consistir, to consist, tardar, to delay, be slow, insistir, to insist, etc.), para, to express purpose, por to express cause, sin, con, etc. It is impossible to formulate rules to cover all cases. In general, it is best to memorize each individual usage that differs from the English. 430.

21. Que is found after tener before an infinitive to express compulsion or strong obligation to do the act of the infinitive: tuve que hacerlo, I had to do it. Compare deber, 425, 426. 431.

22. After many indefinite pronouns which usually denote quantity, such as nada, algo, mucho, etc., que is the connective before the infinitive: tengo mucho que hacer, I have much to do; no tiene nada que ver con eso, he has nothing to do with that. This construction is also found after nouns: tengo una lecciOn que estudiar, I have a lesson to study.