येन गच्छामि — यानेन, मार्गेण
By bus, by boat, by which road — instrumental of means

यानेन गच्छामि, नौकया गच्छामि — तृतीयायाः सर्वाणि रूपाणि।

Vehicles and routes take तृतीया too — and you meet the full instrumental family.

श्रवणम् · Listen

नगरयात्रा
 रमा —  श्वः अहं नगरं गच्छामि। 
Tomorrow I am going to the city.  
 सीता —  केन गच्छसि? यानेन वा? 
How will you go? By bus?  
 रमा —  न, अहं नौकया गच्छामि। नदी समीपे अस्ति। 
No, I am going by boat. The river is close by.  
 सीता —  एकाकिनी गच्छसि वा? 
Going alone?  
 रमा —  न, गुरुणा सह गच्छामि। 
No, I am going with the teacher.  
 सीता —  अहं तु पादाभ्यां गच्छामि — एतेन मार्गेण नगरं समीपम् एव! 
I just walk — by this road the city is quite near!  

विवरणम् · Explanation

येन यानेन, येन मार्गेण च गच्छामः, तत् अपि तृतीयायाम् — यानेन गच्छामि, नौकया गच्छामि, एतेन मार्गेण गच्छामि। “पादाभ्यां गच्छामि” इति श्रुत्वा एव अभ्यस्यतु — “पादैः” इति द्वयोः पादयोः रूपम्।

The vehicle you travel by and the road you travel along are also instruments — यानेन, नौकया, एतेन मार्गेण. The set phrase पादाभ्यां गच्छामि (I go on foot, literally by the two feet) uses a dual form — learn it as a chunk.

तृतीयायाः लघुसूची — रामेण · हरिणा · गुरुणा · रमया · नद्या · फलेन। वाक्येषु एव स्मरतु — हरिणा सह, गुरुणा सह, रमया सह, नद्या गच्छामि — नदीमार्गेण इति अर्थः।

Your instrumental mini-chain: रामेण · हरिणा · गुरुणा · रमया · नद्या · फलेन. Notice ‑इ and ‑उ words take ‑णा (हरिणा, गुरुणा), the feminines take ‑या (रमया, नद्या). Remember them inside phrases like गुरुणा सह, not as a bare list.

शब्दाः · Vocabulary

शब्दः	Meaning	टिप्पणी · Note
यानम्	vehicle, bus
नौका	boat	तृतीया = नौकया
मार्गः	road, way
पादाभ्याम्	on foot	set phrase — by the two feet
नगरम्	city
श्वः	tomorrow

अभ्यासः · Practice

प्रथमां तृतीयया योजयतु। Match dictionary form with instrumental.

वयं ________ नदीं तरामः। (नौका) We cross the river by boat.

बालकः ________ सह संस्कृतं पठति। (गुरुः) The boy studies Sanskrit with the teacher.

वाक्यं रचयतु — “Tomorrow I go to the city by bus.” Arrange the words.

________ मार्गेण विद्यालयं गच्छसि? — एतेन मार्गेण। By which road do you go to school? — By this road.

वाक्यव्यवहारः · Use it

भवान्/भवती विद्यालयं वा कार्यालयं वा कथं गच्छति? चत्वारि वाक्यानि वदतु — येन यानेन, केन मार्गेण, केन सह, किं विना च गच्छति।

How do you get to school or work? Build four sentences: the vehicle (यानेन / पादाभ्याम्), the road (… मार्गेण), your companion (… सह), and something you never leave without (… विना).