"Aamir saw Peter yesterday."
Translation:आमिर ने कल पीटर को देखा ।
In a previous sentence "I saw elephants" was "मैने हाथी देखे" without को. Could someone explain when to use this post-position with देखना? Thanks.
When you are talking about people or something with its own agency, it is mandatory to use को (or use the dative form if it is a pronoun). Eg: उसने मुझे देखा(He saw me), मैंने भगवान को देखा (I saw God), जूलिया ने पीटर को देखा (Julia saw Peter) etc. This is also seen when you are asking questions. You say तुमने किसको देखा? (Who did you see?) instead of तुमने क्या देखा? (What did you see?)
For everything else, you can either use को or leave it out (in which case the noun becomes a direct object of the verb देखना). So, both मैने हाथी देखे and मैंने हाथियों को देखा are correct. [Notice that in the first sentence, देखना takes the gender and number of हाथी because it is its direct object. In the second sentence, देखना has no direct objects and so is seen in its default singular, masculine form]
The form with the को may be used to distinguish 'look' from 'see'. Also, the को form is often used with pets and other animals when you're not talking about them impersonally.
Thanks a lot. Could you write examples for cases to distinguish "look" from "see" with this form?
The को is used to distinguish 'look' from 'see' only in the case of material objects. For example,
मैंने उसकी तस्वीर देखी - I saw her picture इस तस्वीर को देखो - Look at this picture
When one uses को, there is no direct object in the sentence, only an indirect one. Does it mean that the verb will not change according to the gender and always be masculine?
Yes. Transitive verbs like देखना will take the gender/number of their direct object in the past tense. When there is no direct object, they will be in the singular masculine form - देखा.