Sentences TOO simple to teach various tenses
There are very few useful sentences in the conditional, past perfect, and, to some extent, the imperfect lessons to teach the student what those tenses are for. ALL of the conditional sentences I've encountered so far have just one clause. I can tell from the comments that many readers don't understand what the tenses are and why they're used.
Here is an example from the conditional lesson:
He would have three houses / Él tendría tres casas.
Now I know that the Spanish conditional is used by itself to show speculation, but that is an advanced topic for an English learner that requires context itself.
As for the "normal" use of the English conditional that translates directly to the Spanish: That sentence doesn't really make sense in English without a condition, like this:
If he saved his money, he would have three houses.
Should I move this to "Troubleshooting"?
I think it's ok for Duo to concentrate on the "what" (as in what form does the verb phrase 'he would have' take in Spanish, without worrying too much about the "why" (as in why you'd use it in the first place). I think it's understood that you should know why you'd use it, and in any case there are explanatory pages for many of the sections.
As far as a grammatical sentence goes though, "he would have three houses" is fine on its own. It could be said in response to a question "What do you think he would have if he saved his money?"
One problem I can see with making people do the full sentence is that they could easily get the "If he saved his money" part wrong, which isn't conditional, get the conditional part right, diverting their attention away from what they're supposed to be learning in that particular lesson.
The Spanish conditional is used in more situations than the English conditional. Any hypothetical situation uses the conditional in Spanish. There does not have to be a conditional clause stated in Spanish or in English. When something is in the future, it is already maybe going to happen and maybe not, although sometimes you make it clear that you plan to make it happen. "I will go there." or "I am going there" seem to leave no room for doubt, but "I would go there." is inherently just a possibility. What could make it happen? What could make it not happen? Those would be the conditions. So "I could go there" is often conditional in Spanish, unless it specifically is being used to mean "I have the ability to go there." as a mere statement. "Let's plan our route. Do you think you can go up this hill in your wheelchair? Yes, I could go there." (This is planned and I will be able to go there. No doubt involved.) "Are you going to the new store? I could go there." (It is possible that I will, if I feel like it or I might just decide to go elsewhere. It is unknown what will happen. It really means "I would be able to go there.")
(So "would" is a big tip off for conditional, unless of course, you are stating "When I was a little boy, I would sit on my grandfather's knee and listen to him tell stories for hours." in which case you are saying that you did do it, specifically that you used to do it. So, "would" in the future is the one you are looking for.)
Polite requests "Would you please pass me the salt?" also use the conditional. http://spanish.about.com/cs/verbs/g/conditonalgl.htm http://spanish.about.com/od/verbtenses/a/conditional.htm http://spanish.about.com/od/verbtenses/a/spanish-conditional-tense.htm http://spanish.about.com/od/conjugation/a/conjugation_conditional.htm
allintolearning: Great stuff and good examples. I understand that the conditional is used in many ways that don't correspond to the English conditional.
As for your "grandfather's knee" example, that would be the Spanish imperfect, not conditional: "Cuando era un niño pequeño, me sentaba. . . ."
All these differences in usage—not to mention the usages that are similar to English—buttress my original point, that at least some quiz sentences should have a little more context (just a short clause will do in most cases) to demonstrate the various usages and implications of the Spanish conditional (or pluperfect, or imperfect, etc.).