D-Form and Te-imasu

Hello! I am confused with the following, please kindly advise! :)
田中さんがコーヒーをのんでいるとおもいます。
田中さんがコーヒーをのむとおもいます。

May I know what is the difference between these 2 sentences? Can we use D-Form and Te-imasu interchangeably? I understand that D-Form is present tense and informal form and te-imasu can be used for present continuous and habitual action. Another example is:

おとこのひとはこうえんをはしる。
おとこのひとはこうえんをはしっています。

Please kindly advise. Many many thanks!

FIrst of all, do you mean "dictionary form" when you say D Form? :)

田中さんがコーヒーをのんでいるとおもいます。I think Tanaka-san is drinking coffee (now).
田中さんがコーヒーをのむとおもいます。I think Tanaka-san will drink coffee (sometime soon).

おとこのひとはこうえんをはしる。A man runs in the park.
おとこのひとはこうえんをはしっています。A man is running in the park (now, as we speak).


When dictionary form is used as it is as the main verb, that's informal "speech" (it by itself is not "informal form").

Hello AK!
Yes, I mean D-Form is Dictionary Form.
Thank you! It is very clear and easy to understand. My teacher was using them interchangeably that confuses me.

Thank you again!

what if "the man ran in the park"?

in "おとこ の ひと は こうえん を はしりいまして" can "はして　います" be used? (maybe no?)

AssassinWarrior,

If you want to say the man "ran" (past) in the park, then it will be
おとこ　の　ひと　は　こうえん　を　はしりました。
If you want to say the man "was running" in the park:
おとこ　の　ひと　は　こうえん　を　はしっていました。

i guess i had some typos..thanks for the explaining

oh...now i see the difference!