When o use half letters.

when do you use half characters for a word. What are the rules for this?

e.g. क्या 

Understand the rule as given below for using half letter.

Conjuncts :   When  two consonants are pronounced without a Vowel  between them.
( In our website "Writing Lessons; has details of Vowel and Consonants)

When the first letter of a conjunct contains a vertical line, The vertical line is deleted, then the modified consonant symbol is conjoined to the second consonant symbol. 

Please find below examples of All List of consonants having vertical line 

ख + य = ख्य ,  ख्याति  - Fame  
ग + य  =   ग्य , ग्यारह - Eleven 
च+च =  च्चा, सच्चा  - True
ज+व = ज़्व , ज्वाला - blaze
ण+ड =ण्ड. अण्डा - egg
त+ म = त्मा , आत्मा -Soul
ध+य = ध्य, ध्यान - Care /Attention
न + द= न्द , हिन्दी - Hindi
प + त =  प्त , सप्ताह - Week
ब + ज = ब्ज ,  सब्जी - Vegetable 
भ + य =भ्य,  सभ्य  - Decent
म+ भ = म्भ , आरम्भ  - Begining
ल + प =  ल्प,  संकल्प - determination/Oath
 व + य  = व्य, व्यस्त - Busy 
 श +क =  इश्क, - passionate love 
स + त   = , स्त , व्यस्त  - Busy

 क and फ are also follow the above rule ( not vertical line in these cases)
 क + य = क्य, क्यों
 फ  + त = फ्त, मुफ्त