Yes, you can add mal- to any word to form its opposite :)
And mostly that's what you do - there are some pairs of opposites where both separate words are in common use, but often, one of the opposites is only poetic or is not there at all and you use mal- to form the opposte, as with malfermi "OPP-close = open", malgranda "OPP-big = small", maljuna "OPP-young = old", malsana "OPP-healthy = ill", maldekstra "OPP-right = left", and so on.
Sometimes, people even add mal- as a joke when it isn't usually used, e.g. maltrinki "OPP-drink" for "piss" or malmanĝi "OPP-eat" for "throw up".
Congratulations on your development of an Esperanto sense of humor!
Trying to channel Zamenhof, I think he introduced the "mal-" prefix firstly to reduce the number of root words, which are easy enough for most Europeans to remember, but difficult for many non-Europeans who don't already have a good command of a European language; secondly, and related to this, he wanted to allow some leeway for non-Europeans to use this prefix to create comprehensible words even where there is a root (unknown to or forgotten by the non-European Esperantist) to cover the same concept in Esperanto.
No, it is not funny at all, Salivanto. You clearly have no shame stalking me on the comments pages here. Your behaviour is petty and malicious. Think at least of how this will look to any potential pupils (since your presence on these pages is presumably, at least in part, to attract pupils). In our earliest exchanges, you gave zero help - you made a suggestion that would be suitable for a monoglot English speaker learning his first foreign language. You have never bothered to engage with any substantial point that I have made. You exaggerated and misrepresented matters in your previous swipe (which lacked a "reply" option).
I am asking you again to leave me alone.
With regards to your specific question -- it only applies to some words. Some words have no opposite (malarbo, malsegxo, malpomo), some words don't have a clear opposite (malknabo, malbrui). Other words have a clear opposite but are expressed by separate words (blanka/❤❤❤❤❤, nordo/sudo).
Neverthless, mal- is very useful and can be used to make any opposite, as long as the opposite is clear.
Translations of examples above - untree, unchair, unapple, unboy, unmake a ruckus, black/white, north/south.
In the meaning "have an opinion", "think" is not usually used in the present continuous tense.
You can say "I am thinking about it" if you want to emphasise the cogitation and mental work behind it, but for "I assume, I am of the opinion", it's usually "I think (that)..." - much as we say "I see that house" and "I have a pencil" rather than "I am seeing that house, I am having a pencil".
It sounds good to me.
There are three things that happen when we accent a syllable.
- we say it louder
- we hold it for a longer duration
- we use a higher pitch
To my ear (fluent Esperanto speaker) it sounds like he is correctly accenting the syllable, although there seems to be equal or higher pitch on "vas" - which might be what your ear is picking up on. Two out of three ain't bad.
Are there any rules around the "base" word? Why is it malgranda instead of something like "malpequena" or malfermi instead of "malaperti"?
Is it just that Duolingo is teaching a simpler vocabulary and these exist?
It seems like the goal was to make Esperanto simple and easy to learn by cutting two words into one word with or without the "mal-" prefix, but reading through the comments, it feels arbitrary, even biased sometimes (thinking about "right" and "left").